When a teenage girl disappears from a north London suburb a few days before Christmas, Detective Sergeant Effie Strongitharm puts would-be cult leader and reputed exorcist Nigel Tapster on her list of people to be questioned. But when Effie witnesses Tapster's agonizing death during a church service, she needs to ask a different question: What holy terror spiked the sacraments with strychnine? With her mentor Detective Superintendent Mallard battling forced retirement, Effie turns to children's book writer Oliver Swithin to help her in a double quest—to bring the girl home and the murderer to justice in time for Christmas. But is there a connection between the cases? And what does any of this have to do with a Scotland Yard Commissioner's personal hygiene, a six-year-old Hell's Angel, a Guide to beastly behavior featuring Finsbury the Ferret, a touch of Shakespeare and the return of the mysterious, virtually invisible Underwood Tooth?