Yanno, my first reaction about a nic/Mavra team up was meh. But I could see Nic thinking the only real hope for reality is banding the powers of "dark" together to fight the incursion from outside. After all, the gates are protected by Mab.

If he was working from that line of thinking, it would more or less explain all of his actions. He has had 2000 years to snatch up power, but he doesn't seem to go in for controlling or toppling governments, he could probably own most of a continent by now if he wanted to. But in the last ten years he has made a play for power from the plague curse, the archive, and the artifacts in the vault. Certainly sounds like he is accelerating his grab for power.

He knows a war is coming and it even sounds like we know what side he is on. It would be precisely within his character to think that he is realities only hope, and uniting other powers behind him (dark ones obviously) is how he can do it. And if he happens to come out of it with enough power to make himself god-king of the universe in the aftermath,
So much the better.

Hmm... interesting... though I've had the impression (for no particular reason I can cite) that when Harry is "below the island" where the "cells" are located that he's more in a "pocket dimension" rather than some general "place" in the NN - sort like Agatha Hagglethorn's personal demesne.

It would make sense to have very limited access - if DR doesn't let you in you don't get there.  It prevents "breakout" attempts because there's no way to "tunnel" in from elsewhere, etc.

But even her pocket dimension was technically a part of the never never.

But the main thing I was thinking was that he could gain all kinds of knowledge of ways and things. We know there are ways onto the island, the traitor and one other shadowy person took on to the island in TC. If he can figure out the way to some of the places DR touches that would be really useful to him.

But that is just a start. If he were able to get some creatures to the DR part of the never never, he could learn a massive amount of information about them, potentially. Or maybe some information on the nature of the never never itself. The spirit realm is a tricksy place and he would have an even bigger advantage with his intellectus there than he gets here. And itd be just plain fun .

Im inclined to think that it is not partially in the never never, if for no other reason than it would be just one more way into the prison. Prisons with a lot of entrances and exits arent as secure.

While they could summon, the powerful entities potentially ignore the summons. The power of the island, and the darkness of the power, could be enough force and affinity allow for no summon to be unanswered. It is one thing for a creature to be summoned, it is another for them to be bound. So once brought to the island, the island and warden would be forced to fight. Admitted on the island, the warden has access to great power, but fighting well worth beings will allays be tricky.
 If summoned, would they only be brought to the surface or into the well? It does not seem secure to bring an unbound prisoner into the cell block.

Having the proper bait to get the beings to the island is probably that tricky part. As for binding the creature once its there. Demonreach apparently had the power to grab and bind a (more or less) full-powered Mab once she was physically standing on the island. DR has some chops. Of course the beings worth imprisoning on the island will have a lot of power too, and will definitely fight back. But Demonreach's power in such a conflict would be so much greater than Harry's that he would probably factor very little into the fight. IIRC correctly, Harry said something to the effect of wanting to be somewhere over the horizon if DR started swinging in earnest against an enemy.

Unless he had a Name to work with, or something. Or, maybe there is something in the islands architecture that we dont know about for such a fight, like weaponizing the stones from the cottage that repelled shagnasty. The real question is whether or not we will ever actually get to see such a fight. I really really hope so .

Which to me implies that there is only one capital "Warden" especially considering the line in Eb's journal.

As for the cloak WoJ, that's more ambiguous. 

To me, that WoJ implies that there are non-human guardians acting as wardens of Demonreach on the never never side. That is something I hadn't considered before and something that Harry should investigate, like, yesterday.

Id think they had some kind of other solution to the the waste problem than miles and miles of pipes through stone. Not that that is not possible, but obviously plenty of NEW dwellings have been built, and if so they would have no way of connecting them now with the old sewer systems, since the means of shaping the spirestone seems to be lost in history.

My guess is they have something that quickly dilute/converts the waste into something else. IE: you go in a pot, press a button and a kind of chemical solutions rushes in and combines with the waste and alters it into something less toxic (sand was mentioned, it could be broken down into water, etc.) Then whatever the byproduct is of the chemical reaction is either pure liquid and runs out through some (above the stone) pipes into large tanks to be collected for use, or if its solid, just gets collected once a day or every few days and thrown in the trash or a place to be recycled for further use.

Or, since this is steampunk, the waste is combined with a chemical to liquefy it completely, then a heating crystal evaporates it and the steam is pushed through some turbines to generate power or some other gadgetry before exiting the habble through the ventilation tunnels.

Dammit. I REALLY like this theory . Very very sad because Bayard is one of my favorite characters. Which is, of course, a perfect reason for him to be the traitor.

I agree with the earlier post about Abigail being mentioned more than was necessary being of interest, maybe she is the traitor.

The one thing I can think of to counter any of it is that both the Spirearch and Grimm mention that they think the traitor is in the Guard. Grimm even specifically says that as being one of the reasons Addison used the criminal guilds of Landing to be ready for a potential attack, and did not dispatch additional members of the Guard. Of course they could be wrong, and an aristocrat or high ranking member of the fleet would certainly be able to find ways of their own to gather such information. But for the moment they are proceeding from the assumption that the spy is in the Guard, specifically.

(oh hey, what about the Spirearch's batman?)

Mac does raise an eyebrow at Harry's insistence on drinking heavily in Changes and I think thumbed the keys away from him iirc. I'm sure its plenty potent.

In changes he doesn't drink beer he asks for liquor. I don't think it specifies a type but fairly safe to assume it's whiskey.

However in White night he gets several beers and gets tipsy. And Mac takes his keys