Likely Bomb Drops

[BobbyWac]

I also wouldn't be surprised if Eb "dies" in this book, via the Blackstaff returning to Mother Winter. Then we see the emotional toll on Harry, but Eb isn't actually dead. Instead now working in the background as a spy for Mother Winter as repayment for Eb using her walking stick for so long.

[Cozarkian]

Thought of one.

Ancient Mai reveals herself to be a staunch ally of Harry because of his connection to Mouse. She will volunteer to go on a negotiation mission as the WC rep with Harry. When all hell breaks loose she will reveal some secrets about Mouse with a promise to explain everything later. Naturally, she will die before having the opportunity.

Another - Harry persuades Mortimer Butters to attend the Peace Talks and gets him status as a representative of minor talents / the Paranet. Butters doing that makes more sense, but isn't much of a bomb.

Three, the FBI shows up.