I have long thought Mavra was quietly paying back old insults and removing her rivals. She certainly is playing a long game.

Mavra is really interesting to me. I think she is one of the better examples of a theory I have that there are competing villains with their own agendas. Perhaps one group that simply wants unrestrained power - the anarchists. Others that want the end of reality - Outsider backed team. And others still that just desire to rule reality themselves - Hell backed team. But I think they are all intermingled, appearing to work together but actually running games on each other. I think Mavra is more aligned with the Anarchists, which Maggie Le Fay was originally a part of (along with Justin and several others). I think the Outsider team is taking advantage of certain peoples agendas for their own ends.

I have a very tenuous theory, but it feels right.

When Harry asks Binder who Madeline Raith is working for (in Turn Coat) Binder says he never knew. All he did know was 

it was some bloke with a lot of money. I never talked to him. When she was on the phone with him, they spoke English. He wasn’t a native speaker. Sounded like he’d learned it from a Continental.

Continental tends to mean Europe. Christos is Greek and described to wear wealthy designer suits underneath his Wizard robe.

Just a thought.

cptnspldng - I am a bit of a conspiracy theorist here. I don't believe Justin died as it never happened on screen. In fact - Harry so rarely goes into detail about that fight (remembering the ENTIRE SERIES is him talking about his past, it is almost like he is avoiding it on purpose). I have a few reasons why that night is a blur - remember Harry didn't even recollect his encounter with the Walker HWWBH until he was dead and the Leanansidhe showed him. I am of the opinion that:
1. Harry (the narrator) recalls that at the time did not properly remember that fight (even if he thought he did - that's the tricky thing about memory).
2. Harry doesn't recall that fight as it truly was for more than mundane reasons (e.g. PTSD, poor memory recording abilities etc.) but because of interference (perhaps by himself, a time-traveler, some other monster/being or perhaps Justin himself). Never forget that while the binding on his body was one Harry himself had figured out, Justin was getting in his head even then.

Mr Death is correct in that the fight is in two parts (mostly because of inconsistency on JB's part). Part 1 is when he comes home from school and find Elaine being weird on the couch and Justin tries to convince him willingly into the fold, they fight and he uses the force of Justin's spell to smash him out a window and escape. Justin then sends the Walker to kill him (though it is implied and Harry muses that perhaps it was the Walker running the show) and he defeats the Walker - with a mixture of magic fire and gas explosion (which even Dresden later realises should not have worked - especially when you take into account this thing is supposed to be Uriel-level). Harry then goes back angry and duels Justin and is subdued by Elaine's binding. Justin then attempts to perform some strange ritual involving Harry consuming human blood for an unknown purpose, Harry breaks free and then...we only know that Harry uses fire to burn the house down. We have no other information. We never even had a body of either Elaine or Justin. Harry presumes them both dead for many years until Grave Peril where he has a dream where he realises Elaine might be alive. Then she shows up in the next book, a year-ish later. We only have Harry's word that Justin died (which was highly doubted at the time). Justin is Dead in Harry's mind because he wants it that way. Not because it is. See that whole passage about eye witness accounts in the series/remember Harry was just as sure Elaine was dead.

But I am of the opinion that considering how much Jim has said he is dead, he probably isn't. Jim wants to throw us off the scent. Not to mention Jim has said Death is a squishy line in the Dresdenverse. More like a threshold, you can cross and come back. Few do it, but it can be done. Not to mention, we know from the series that once you cross that threshold, you don't just stop existing. You go into the varying levels of the afterlife, beginning at being a spirit/ghost and moving on into the varying Heaven's and Hell's and all the inbetweens. Also Mab has said Death is not black but grey, it is a spectrum not a line. Which makes a lot of sense really.

So even if Justin is dead or has died - that is not to say he has stopped existing or is not involved in events behind the scenes. He may have not died, or he may have resurrected himself, or perhaps he works as a ghost or somesuch. But believe me, he isn't out for the count. He had a plan.

How do you mean Bob is unreliable, morris? I have always thought his theory to be sound. Hell, he has explained more magical theory than most and he even knew how to kill an immortal (which so far very few other mortals know). His literary purpose is somewhat of a "talking head" (hence why he is a talking skull - it was a joke that he made to annoy his writing teacher). I think the only time he has kept info from Harry was about the Kemmler stuff, though he does get shaky around Mab.

Is Thomas unreliable? That is a big question. He frequently has come through for Harry. He does keep him out of the Oblivion War - but that is because it would be completely stupid to include him. At times, he has shown reluctance to help Dresden like after he got tortured. But I would say he has been compromised - like a veteran with PTSD. It happens. But overall he has always been in Dresden's corner.

As for the limp - I mean Jim has literally given his word-for-word reason that the island has a limp. No need to look for another reason - we have the reason. Unless you mean the ice-age cause the buildings to crumble. Maybe the buildings are that old. I think it more likely Jim is referring to what the island was BEFORE it was an island - a mound and before that, a pit. A pit where perhaps someone through a bunch of demons or nasty creatures and built a hill on top. Someone like Raphael "the Demon Binder" perhaps. Which should answer how those prisoners got in there.

I think the Gates wern't always Gates, per se. They resemble Fairy architecture because Fairy control the Gates. They likely resembled something more Nordic when it was the Norse Gods (or Jotuns - depending on your theory). WOJ is that the Gates look like Gates to Harry because that is how he "sees" them - his mind can't process the true reality of them. Likely the truest way to describe them that fits into Jim's mythology is the threshold to Reality (which is why we have all the stuff about invitations, hospitality etc being so important both magically and socially). If the Gates are the threshold to Reality - the natural conclusion is they were built by the Creator (which may or may not be the Almighty/something that resembles it). WOJ is that the Almighty built his Creation and told the Outsiders to stay out and so they did, but he doesn't stop us from letting them in.

Con - you definitely are on to something. I think WOJ is the Gates have an awareness, but it only really amounts to "I AM HERE". Demonreach is vastly more complex in that sense. But I wouldn't be surprised if the Gates/Walls have their own Genius Loci - from which Rashid gets assistance. One could argue even that that might be the Mothers - specifically Winter. Power has purpose after all. The Mothers do have intellectus - which does seem to be shared. Food for thought.

I do suspect the Gatekeeper (like being The Warden or The Merlin) is a mantle. It might not be a big power boost, but likely it comes with the Eye and maybe some other tricks. Who knows what the Merlin mantle comes with, likely knowledge. Remember Jim has said all the Senior Council have their own sources of power, but they keep them secret. The Blackstaff - mostly the staff more than a "mantle" in the magical sense I imagine.
 

Cowl is Justin and Elaine is Kumori. Here is why I think it adds up.

Cowl:
1. Cowl has appeared in several books - first notable one is Death Masks at the Bianca's ball. He delivers a gift (possibly nemfected) to several guests, but only confirmed through Mab about the Leansidhe. Morgana's Athame is traded for Amoracchius (Excalibur).
2. In Dead Beat Cowl mentions many things of significance happened that night, Dresden is only aware of a few of them. Cowl likely conspired with Mavra and Bianca and her progenitor (Ortega), who's wife Ariana was part of the group that Margaret Le Fey, the White King, and possibly Justin Dumorne were all a part of. A group that might have decided it was time for the White Council to end.
3. A shadowy figure sponsors and is seen in White Knight. Harry seems to recognise his magic as Cowl's. In this book, the Circle is mentioned for the first time.
4. Cowl is an expert at Evocation, Neuromancy, Veils, Ways and Necromancy. He also mentions his skill at swordplay. Why would Cowl have a sword? Most wizards do not carry them. But an ex-Warden would. All his magical skills and talents would make him an excellent warden (excluding the fact he can't use Necromancy).
5. Justin is likely a skilled Neuromancer/Psychomancer - he enthralls Elaine before Harry gets to the confrontation.
6. Justin was in the assault on Kemmler. Cowl says he despised the "mad man" Kemmler, despite being his student. He may well have taken the opportunity to erase his enemy for his own ends.
7. Justin was Simon's apprentice. It is stated in Summer Knight that Simon's fortress was impregnable, and the Warden's forensics suggest that someone let them in past the defences. Eb says it would still have required someone who knew the place inside out. Justin is only discounted on being dead, but otherwise as a rogue Warden and Warlock would have been a candidate, who the Council suspect passed on the knowledge to Harry. Now we know that it wasn't Harry - so it doesn't leave much leeway.
9. Simon is said to have been found dead, along with the brute squad. Whilst it doesn't explicitly state his body was found, it would be a hell of a thing for them not to notice his missing corpse. A whole plot point in the series is built around how intolerable it would be to have a high-level wizard turned to the enemy. A missing Senior Council member might have provoked a stronger reaction.
10. We only have Harry's word that Justin died, and that he fought Justin in earnest. Most people thought is unlikely he beat Justin. Fires in stories tend to be useful covers for other events, a physical symbol of chaos.
11. Jim says Justin is dead. D-E-D dead. He has also said not to trust a word he says. JB has also described death as "a squishy line in the Dresdenverse"
12. Many characters, including Mab, have said Death is a spectrum.
13. Harry believed Elaine was dead. Harry was wrong. If he was wrong about her...
14. From a writing perspective, consider Star Wars (one of Jim's favourite stories). Luke is raised an orphan by others, his lovely aunt and uncle. He then goes on an apprenticeship with a wise old mentor. He is told his father was a Jedi, who his most feared enemy killed. Vader reveals he is Lukes father, which Luke is in denial about but realises must be true. Obi-wan does the fae-speak of half truths (When your father became Vader, he killed Anakin Skywalker). The trope of Harry thinking his foster father and first mentor is dead, who actually isn't would be a good technique and mess with Dresden's psychology majorly.
15. Cowl hides his face, the other Necromancer's do not. Harry suspects White Council. He might be right, but likely that is not the only reason. They even distort their voices. Vader hides his face too - and was a jedi once. Luke just did not know it.
16. Cowl wishes to end Death. Why? The Outsiders might want that, perhaps it would limit the power of TWG. But why would Cowl? Kumori seems to believe him. I suspect it is because he is traumatized by the Death of someone he loved.
17. Justin and Cowl both have links to HWWBH.
18. If Justin is dead, why no Death Curse?
19. Elaine is the most likely candidate for Kumori (I think she might also be the prevailing fan theory - but I will have to check). If Elaine is Kumori most of the other candidates for Cowl don't make much sense. Justin fits better than the others.

Kumori:
1. Kumori is tall enough to hold a knife to Harry's neck - Harry is 6'9" roughly so not an easy feat.
2. Elaine is described as being tall, tall enough she only has to stretch a little to kiss him on the cheek.
3. Elaine is described as being a better at magic than Harry, while Harry is brawnier. She is skillful enough she is not worried about people seeing through her veils.
4. Kumori seems to use less brawn and more subtler magic than Cowl; less of a duelist but still deadly.
5. Kumori is a distinctly japanese name.
6. Elaine uses japanese as her magic words.
7. Kumori shows compassion - she resurrects a dead gunman of Marcone's for apparently no other reason than because she thinks she should.
8. Elaine has shown much compassion for her fellows, whilst still distrusting the institution of the White Council.
9. Elaine was the Emmisary of Summer/Harry's opposite. She says she was part of the Summer Court for a long time. Summer has been involved unusually in the books. Mostly ambivalent or directly in contest with Dresden. Rarely against the foes of Dresden.
10. Kumori and Elaine show compassion for Dresden, but not so much that it impedes their goals. Kumori even goes out of her way to warn him in the stairwell but they end up agreeing to disagree when she tries to convince him to leave.
11. In that same scene, Kumori tells him to remove his force ring. He puts this down to being White Council trained enough to recognise it for what it is. But if Kumori is Elaine, then she simply knows that he has it. Keep in mind, on no other occasion has anyone recognised or been aware of that ring nor do many other wizards/sorcerers use such things. Elaine does however, a product of her shared training with Justin.
12. WOJ is that Kumori's identity will really hurt Dresden. Griffyn's theory relating to the Batman/Catwoman scene, I think it certainly adds flavour even if the scene in the books ends up quite different. I suspect the scene will be a gut punch.

Bit of a wild theory here. I believe Justin was in love with Maggie. They had a relationship and they both felt the White Council was too harsh and too rigid. Maggie and Justin had two children - Elaine and Harry (perhaps twins?). Elaine is older than Harry - he is always referred to as Margaret's youngest. When Maggie was killed by the White Court - Justin was furious. But he could not yet move against them. He finally gets his children back when Malcolm died. He raises them to be his disciples and enforces but it goes wrong and he either dies and is revived or fakes his own death. He finally gets his revenge by "accidentally" murdering half the White Court when his uber-ghouls start murdering everyone. He definitely would want to end Death as he is still grieving Maggie.

From a writing perspective (and fitting nicely with the Star Wars inspiration) - it would be a major shock to discover not only is Justin alive, but he is Cowl and been orchestrating all the terrible stuff in Dresden's life. It would also majorly freak Dresden out that he was in a relationship with his sister, something Justin would have definitely encouraged (like a good cult leader). It also matches the weird Luke-Leia thing. Finally, you might argue Dresden should have recognised Justin's magic. I think he sort of did without realising it. Cowl's magic is human, with a bit of Dark Magic in it - unlike the Mavra or even the Corpsetaker. Harry recognises so is his, which makes sense when you realise he was taught all the basics by Justin/Cowl. I also believe Justin will likely kill Ebenezar while he tries to protect Harry. Very common trope. Harry might find it very hard to be good when he realises his whole life is a lie, he was born to be a weapon, he commited incest (potentially) and that his mother was in on it for a long time. Harry is given power over Outsiders. Yes he uses this as a weapon - but perhaps the real purpose is to be a leader (very Hellboy in my mind).

I did just make a thread about this but it got a bit sidetracked and I also thought the theory should be in the appropriate thread. I also really enjoyed DonBugen's TT theory, excellent write up. It could fit but I think some of the connections were a little fragile and could be accounted for inconsistencies and weakness's in JB's writing. I also think DonBugen's analysis of the Darkhallow was pretty bang on.

morriswalters - I hope I haven't caused you offense. Perhaps we will discuss it further one day. And by "all of the fey" you mean some I think...at that particular battle several characters and creatures were described specifically using other weapons (e.g trolls with clubs, fey with spears, Winter Lady and Queen etc.) But really we are talking about humans, not creatures of magic. Specifically Wizards - who largely rely on magic for combat. My memory of the humans that use swords are (the 4 knights of the cross - butters only technically, Nicodemus himself - I don't recall ANY other Denarians using swords as most rely on their Fallen's monster form, Lloyd Slate and Fix - as Winter and Summer Knight respectively) But most don't (the Denarian squires use guns, Kincaid doesn't use any swords - though he isn't strictly speaking human, none of the cops other than Murphy, None of the Black Court Vampires, only some of the Reds - they also use obsidian axes and blades rather than traditional swords, the White Court Vampires do - but they also use guns and explosives just as much and are considered the most modern of the Vampire Courts, Charity uses hammers, Molly doesn't use swords, none of the priests, not Marcone or his people apart from Gard who is probably a Valkyrie etc.)

Harry likely learned fencing like everyone else does - in a class. Fencing classes are everywhere. But the only teach fencing as a sport, anyone old school (like Morgan or Luccio or Grevane etc.) would have learned it not for sport but for defense. Warden's likely learn it from each other. He has fought twice I believe as he normally likes to express Earth Magic through his sword cane - primarily electromagnetism. He has used the blade though, I will have a search around for the text. But he does it rarely, as like most wizards he relies heavily on magic in combat. Sword users that have been described, especially humans are in the minority in the series. Don't get me wrong, I love sword fights and duels. Great stuff to watch, I have seen many acted out and been to many fencing competitions not to mention watching many online. I have actually seen the JB proposal which was very sweet. But none of this means that Swords are common to humans (especially magic humans) in the series.

Maz - I think you are confusing Harry piercing veils with magic and his powers of deduction. He recognised Talos and Korrick through process of elimination (he knew Auror was behind the theft of power, meaning her people would be the one's with her but he didn't "see through" the veils sphysically. He would have had to use his Sight). I believe in the Mavra case you are referring to is when he first meets her at Bianca's ball. In that case he used his magical "sense" to work out where an invisible person was - but again did not "see" through the veil. He would have had to call upon his Sight. Which he does to Ariana during the duel with her - but any practitioner with the Sight could do such a thing. It is hardly unique to Harry. He is frequently missing veils actually (Cowl and Kumori snuck up on him, Elaine and Korrick catch him straight off guard despite almost being on top of him, Martha Liberty was only feet from him an Ebenezar yet he wasn't even slightly aware of her and Listen's to Wind etc.)

Would you recognise her? Even with a physical disguise that obscured her body shape and face, and a magic voice distorter?  Its conjecture anyway. The fact is Harry does not recognise Kumori. We can only speculate as to why. Perhaps he wouldn't recognise Faith or Jenny after so many years even without all the other disguises, but we cannot know this. And likely if Faith, Jenny and Elaine were all in a room with him wearing a simple mask he probably would only recognise Elaine if anyone. Because of how well he knows her. But if Elaine were Kumori, all the more reason to hide every recognisable part of herself. You don't argue the impact of Elaine, but we do have the facts that support Elaine over the other two (including that the reveal of Kumori will hurt Harry alot) and yet as I understand your argument to be it couldn't be Elaine because Harry is hyper-observant. But if Kumori's disguise trumps Harry's observational skills then your only reason that it couldn't be Elaine falls apart. Realistically if you were a detective trying to work out who Kumori was would you pick the person who most fit the facts or pick a person who might fit one or two of the facts? Does it really stretch belief that it was Elaine in front of him the whole time in disguise? It is a common trope. Not to mention, it actually happened already with Elaine in Summer Knight. She was with the villains from the start yet he couldn't see it at all. Harry has a huge blind spot when it comes to women, especially in the earlier books and especially ones who seem vulnerable. It is constantly used against him.

Raidem - Ah yes I remember that theory. It would be an excellent betrayal. However as we don't yet know how time travel works in the series, it is still a bit of a long shot. Remember Vadderung says that it is difficult and extremely dangerous to mess with the past - not to mention the Law of Conservation of History (as Harry calls it - the effect Odin describes is that events in the past tend to happen always the same way as there is a quality similar to inertia at work). However I could see it being regular old Maggie Snr who has transcended her Death.
I haven't yet read the Amber Chronicles - it is on my to-do list - but in Amber is the lady that returns a significant character? And does is her return a major plot point? Does it have a long lasting effect on the main character? Was there a lot of foreshadowing? And same applies to the girlfriend. And by "bad actor" do you mean villain or is that a specific type of being or class that exists in the Amber Chronicles?

Thank you Snark Knight, for addressing a few of those points. As SK says, Harry is only observant when it suits the plot. Harry completely failed to notice Molly being in love with him, or that the Grey Lady was Molly (and Leah for that matter), he failed to recognise Lasciel's return in Skin Game and he didn't figure out the Kravos/Nightmare situation until it was way too late - and many more besides. Frequently he only figures these things out at the worst time and only survives by the skin of his teeth. He may eventually figure them out, but I think he has a long way to go. They haven't shown up for a while and I'd say we are well overdue for seeing them so likely another encounter will be in the coming book.

I will do my best to address your points individually:

Groinkick - Very true there is a big difference in that respect, and yes I do feel that Jim wouldn't go into such dark territory normally. However even if that part of my theory is wrong, I believe I am close. Perhaps not twins by blood, but by ritual or some such. I think their connection is a deep one. 

Con - What major plot hole? To your other point, I think it is still reasonable after 10 years roughly that Cowl (if he were Justin) would be interested to see how powerful his former student had become. He also acts rather like a disappointed teacher when Harry proves to be such an unworthy opponent. Justin would be familiar with the Wizard that Harry was at 16, not at 26 (by which point Harry head defeated several dangerous sorcerers, minor demons, started a war with the Red Court and killed one of their nobles, stopped a war between the faerie courts and killed a faerie queen - no minor act considering it hadn't happened for almost 1000 years, and defeated several Denarians). I think he was very interested to see how powerful his former apprentice had become. I had not read that information from the Paranet Papers, which I think is interesting however not evidence enough to exclude Justin or make Simon a more likely Cowl. I was persuaded by the Simon argument for a while but I feel that the theory does not fit the facts as neatly as the Justin Dumorne theory.

Maz - I have answered the first part of your comment above. I am confused somewhat by the fact that you believe that because Harry was a few feet from Kumori he should have recognised her. We know that Cowl and Kumori have gone to great lengths to protect their identities through both physical disguise and magic, why then would Harry the Brawler be able to see through their artifice? They both are likely better at that subtle stuff than Harry is and Justin and Elaine both know how Harry thinks, meaning they could tailor it specifically so that he would personally find it difficult to recognise them. And if Faith or Jenny, why did not recognise them? According to your argument he surely should have recognised them by their voice, smell, magic etc. No, I suspect they are not likely candidates. If you were Jim and you wanted to torture Harry (and by extension his readers) who would you pick to make the most damaging impact? Elaine. He knows Elaine intimately, as you say (though the psychic communication is a spell using neuromancy, he could choose to do it with anyone but it is borderline illegal and he invented it with Elaine and they supposedly trust each other) so the pain of her betrayal will be worse than Faith (who he has met once) or Jenny (who he didn't know anywhere near as well).

Peregrine - A reasonable argument, sure. But being "fairly confident" about something doth buttered no parsnips. Harry is constantly reassessing his history and what he believed. He thought he had no family, he thought his mother and likely his father (malcolm) died of natural causes, he thought Eb was just a nice old wizard who raised him well, he thought Thomas was a terrible monster, he thought Kincaid was human, he thought Leah was out to kill him, he though HWWBH was just some demon (not a major Outsider) etc. What Harry was sure of is only mildly trustworthy at best (especially when it comes to events in his past), not to mention things is only "fairly confident" of. The Name argument is a strong one and my counter is two-fold. One, he wouldn't need to know all of who she is to get her Name right. We are constantly reminded in the earlier books the danger of speaking your Name to another person. You don't need to know exactly what the fish looks like in order to spear it, only to see enough of it and have a good enough method to catch it. A clumsy analogy perhaps, but I am a bit pressed for time. Two, JB unfortunately retcons and creates plot holes all over the shop. I suspect this could be one of them if it came down to it.

morriswalters - SK mostly answered your comment for me. Justin teaches and learned in the school of hard knocks, there are many memories Harry has of his harsh lessons. I suspect he expects everyone to be capable on their own merits. In that particular scenario, one should note Kumori and Elaine are not as major brawlers as other evocation specialists and that the Skavis snuck up on her, which is the bane of every Wizard as JB keeps reiterating. Baby Bickett took me a moment, did you mean the injured Beckett child that Marcone feels responsible for? I mean it is possible but that child wouldn't affect Harry on the personal level someone close to him like Elaine or Susan or Murphy would...it is more a way to get at Marcone if anything. I mean the whole Beckett child thing is not something Harry felt responsible for - he just is sad that it happened.

As for the sword, you must remember how uncommon it is that Wizards fight in direct combat, let alone duels. Harry is definitely an outlier compared to the majority of Wizards and even Wardens. The only reason you see more guns amongst the Wardens is that so many of the old guard were killed and Harry was by far and away leading that pack of new guards carrying modern weapons. Harry having a sword cane that he would use, in any fight, is just plain odd by most standards. Especially as he had it long before he was a Warden. Even only one other Wizard who wasn't a Warden carried a sword, and that was the Corpsetaker. And we really don't know much of his past. Luccio carries a sword not merely as as a secondary combat tool, but as a symbol of office and as an anti-magic tool. Yes it was popular with her generation and with most generations right up until the mid 1900s, but mostly the end of the 1800s. Death by magic (to human mortals) is indeed black magic, but Wardens don't just exist to kill Warlocks. That was mostly Harry's (somewhat justified) prejudices. They do spend a lot of time fighting monsters of the more-than-mortal sort, more so really than they do hunt down Warlocks.

When Mab referred to Death as a spectrum, she was not specifically or even indirectly referring to Necromancy and its ability to bring the dead back to life. I suspect the reason they did not simply raise Bone Tony is that having already tortured and killed him, Grevane arrogantly assumed that he had no more useful information. They picked on Butters as they assumed he might have knowledge that they had missed. Kumori's inability to heal a man who had crossed over does not indicate that could not do so under other circumstances, or that another could not do so using Necromancy. She already had pulled off a feat normally reserved for Gods and other similarly powerful beings. What I believe Mab was referring to was the fact that Mortals believe Death to be the end of existence, which is only true up to a point. By all logic in the Dresden Files, once you die you move on to whatever afterlife awaits you which is another form of existence. True oblivion (where you do not exist at all and are not conscious in anyway) might only exist in certain circumstances, but merely dying in the Mortal plane does not take you there. Perhaps some beings mortals and immortals alike might not have an afterlife (e.g. vampires, gods, demons, faeries and animals) but we have no knowledge of that in the Dresden Files. To answer your last bit about Death Curses - who says he needed to verbalise the Curse? By all accounts only by killing a Wizard before they are aware they are dying (which includes Grevane, who simply refused to recognise he was dying) such as using almost instaneous methods allows you to avoid them. Having been burnt myself, and having witnessed some terrible burning incidents in the line of duty I can tell you that while people freak out, unfortunately you can still think. You are not simply aware of the pain - you are aware of the danger and you are conscious enough to try and take action. It is all the more terrifying because you are aware. Besides, despite how many achievements Harry has achieved killing a highly experienced warden with fire magic because he was scared seems implausible. Justin had survived many engagements and as a Warden would have been very capable of fighting. He may have been caught off guard, but he might have also diverted his remaining strength into surviving. He could have opened a Way or switched bodies - most survivors tend to be the ones that rabbit earlier rather than later. If you wait too long you die. End of.

A few interesting things I would like to point out - Cowl has scarred arms. Scars from what? Burns perhaps? Hell of a feature just to throw in there about Cowl. JB is a lazy writer remember.
Also when Harry talks to his Id - normally there is a secondary message that become relevant later (headaches, lasciel, being too closed off etc). In Dead Beat, he discusses Dumorne with his Id several times. It would fit JB's style to an extent to lay the foundations for Cowl's reveal in the first book he is introduced. 
Finally, I really appreciate the debate from all of you. I enjoy testing the strength of my arguments and hearing others opinions. I would love though if someone can rebut anything or provide an alternative to the points I mentioned better - which some of you have but on balance most of my arguments for their identities remain intact. There has not yet been a strong enough counter-argument or counter-theory that I think rules out my theory as to the identities of Cowl and Kumori. But I am sure someone will have a go and I look forward to the challenge!

Why not? It is messed up, so was that plot point in Star Wars. They never had any kid either - so despite that it is incest it causes no physical trouble. And even though the grew up together from 10 to 16, and even though it might be understandable they had sex (as they were both hormonal teens), it is still weird as even if they wern't blood relatives as they were closer to being brother and sister than just regular friends. I mean they shared the same bedroom, lived in the same house, lived as brother and sister in a way. Being blood related isn't all that stops people having sex (unfortunately history is full of people screwing their relatives, not to mention there are cases of it happening all the time), despite the danger to children born of incest. It is less weird in many ways to start having sex with someone you know a lot less well than a family member. It is very weird grow up with someone in the same house and then start having sex with them, even if you didn't know they were blood you probably still shouldn't be doing it. Knowing that someone is your blood relative should not be the main reason not to sleep with them.

Why Faith Astor? That seems quite out of left field.