Book 8 of The Ghosts -- spoilers ahead for earlier ones.
Caina is attending an official Magesterium event at their chapterhouse -- in her guise as the flighty mistress of the city's coffeehouse's owner -- and thus is there where an expelled wizard appears with a magical knife capable of raising lethal wraiths.
She and Corvalis get dispatched to the only city where the knife could have come from. With the slight complication that you can't actually get into the city for more than seven hundred and seventy-seven beats of your heart, or you will die.
Meanwhile another such attack occurs in New Kyre, and Kylon's fiancee is struck down -- marvelously, not killed. He heads to this city, too.
It includes necromancers who can shift bodies when they die, and one consequence of that; a governor in de facto exile; Claudia living as a physician's assistant and advocating for telling the truth; a deal between Caina and Kylon; and more.