The Invisible Library book 7. Spoilers ahead for the first six.
It opens with Irene and Vale under the English Channel to get a document -- for Vale. They run into nasty cerebral controllers that kill their victims and other issues. Such as -- Irene is very certain that Lord Guantes is dead, and yet meets him.
Meanwhile, Kai and Catherine are waiting for their contact, and Catherine is grumbling because it's not what she expects. Someone tries to poison them, and their contact has the book and is willing to deal, but other complications ensue.
It winds on involving an escape by zeppelin, and a failure to escape by zeppelin, Kai's brother, nuns who treat poison, high alcohol drinks, what Catherine wants and how old she is, werewolves briefly, something rather like necromancy, and more. Also a revelation that I have seen thundering down the tracks for some time, hitting like a freight train.