Shatter the Earth (Cassandra Palmer #10)

Ironically for the time traveling, chief seer of the supernatural world, time has never been on Cassie Palmer's side. There has always seemed to be too much to learn, too much to master, and never enough hours in a day. But the tables have now turned, and the fluctuating timelines of Earth and Faerie are diverging, slowing time in Faerie relative to Earth, and giving humans an advantage for the first time in their war with the fey. It is one they desperately need, for a literal war of the worlds is about to take place. To win, or even to survive, Cassie and her allies, the powerful vampire senator Mircea Basarab and the formidable war mage John Pritkin, will have to pull off their greatest feat yet. And find a way to become more than the sum of their parts.