The attack itself does only one thing. It keeps Mab from attacking the Reds. From an old WOJ.To answer the question why did Mab have Molly brought to Arctis Tor you need only look at the text. It brings all the remaining players to the church were Harry can make the connections he needs to make. The act coalesces his thought process to produce enough of the truth to realize that Molly is the one doing Black Magic. This solves Rashid's mystery.
The secondary effect is to show Harry why Mab did not attack. This is the answer to Eb's question. Somebody with enough power to throw hellfire at the heart of Winter has attacked the Fortress. With the butterfly Harry is able to cast fire and kill the Scarecrow but the attacker killed hundreds of Mab's elite guard.
@Second Aristh
I gave it to you that way because it would be a fairly long dissertation if I hadn't. For instance here is the chain for the attacks by the fetches. While there still are mysteries in Proven Guilty the primary questions posed by Jim are answered in the text. By the end of the arc in Cold Days the rest have been mostly revealed. You know for instance that Rashid works for Mab and that he has the eye. Making Mab the source of the warning. The events around LC are more complex. Why did Jim break it for instance? And why did Lash blow hot and cold. Was the accident an illusion fostered by Lash? If it was sabotage, why? Who was Sandra Marling? Why was the first trial held in Chicago?
This starts with an event at the WWII Cantina in Summer Knight with Harry explaining to Billy.Referring to this.Now connect the dots to the second attack of Proven Guilty. On his way to the screening room Harry is opposed by a ward and Myrk, used to the same effect in Small Favor.And the third attack. Here the lights and alarms are sabotaged in advance of the attack. Now the order of the attacks. Mab sends the fetches to attack Pell. To distract Harry Maeve launches the second attack in the screening room using the same Myrk used in Small Favor and the same binding as she used against Slate. The four fetches are summoned by Maeve in the third attack. Hammer Hands, The Reaper and Scarecrow go to the Carpenters and take Molly while the Scarecrow then goes to the Fool Moon Garage and kills the Jann. Probably at Maeve's direction. The attack against Pell is a pointer to Harry meant to draw Harry's attention. Mab or Maeve, take your pick, had the theater locked up.
I don't buy that the Arctis Tor attack alone was what kept Mab from retaliating against the Reds. Mab won that battle, whatever it was, and she could have called in her reinforcements from the border in moments.
As far as Mab sending a fetch against Pell initially, faerie queens can't just go and order an underling to kill an unaffiliated mortal. That has to fall to a knight.
Idk, there's lots of little things like that that don't add up in PG. I think that the time travel book will definitely spend some time in the background helping to give answers that we're missing. Future!Harry giving Rashid the message to send to him (probably involving Mab and helping initiate her end of the plot and letting her know that Harry would someday be her knight where she can make definitive statements without lying), him causing the car wreck in the beginning for whatever reason, LC issues being resolved. That kind of stuff.