Third book for Irene and Kai and the Library. Spoilers ahead for the earlier ones.
After some library notices about new problems and a letter from Vale complaining about how he needs a good case, the action proper opens with their excursion through an unpleasant France full of revolution to rescue a unique book. About to escape in the Library, they find the gate bursts into flames. The only escape is to use Kai's draconic ability to travel between words, back to the London where she's Librarian in Residence, and there is another gate back. Despite a message from Alberich. . . .
She sends off a pointed message about whether she could have been warned, and the need to warn others, only to find that it is, in fact, a systemic problem, and Alberich is on the move and making threats.
It involves a jaunt to an orderly St. Petersburg, the need to ask Vale to make a choice, a visit to a location that sells exotic beasts, a kidnapping by werewolves, overtures to Irene (some sincere), Kai's family, and more.