I am still mostly on board with the idea that it was Mab who manipulated Thomas for her own four dimensional chess reasons in the greater game. Then another thought came to me, if not Mab,who? One logical candidate for that is Nic. He lost a lot of prestige and power at the end of Skin Game. Damn straight, he wants it back, and he wants revenge. He hosts Andruiel who knows almost everything that is going on, so Nic would know about the dilemma that Thomas and Justine face with her pregnancy. He also has the Grail, with that he could possibly if not heal outright, at least keep the Hunger from eating Justine. While Thomas might know better than to accept a coin, he might agree to blow up the peace talks by an assassination attempt in exchange for keeping Justine safe. Nic gets his revenge against Mab and Harry. He may even think in a perverse way, if he uses the Grail to heal Chicago in the aftermath, he will gain lots of influence and power. He becomes a hero that even Michael would have a hard time faulting, thus putting him in the catbird seat once again.