A knowledge of Oxford is useful but not essential for this light and fantastical read. So is a suspense of belief: The disclaimer proclaims "It is true that the ancient and noble city of Oxford is, of all the towns in England, the likeliest progenitor of unlikely events and persons. But there are limits."
It is 1938. Poet and alumnus of St Christopher's, Richard Cadogan, makes a trip to Oxford. Arriving late in the evening, having hitched a lift from Didcot, Cadogan wanders into a toyshop whose door appears open on Iffley Road, to discover the dead body of an old lady upstairs. He is knocked unconscious and wakes up some hours later. On going to the police, when returning to the scene, the toyshop has vanished, replaced by a grocery store. And there the matter would have rested but for his friend Gervase Fen, a don and amateur sleuth at St Christopher's, who takes it upon himself to investigate. All the action takes place over twenty-four hours, and a number of fairly standard devices crop up - dubious lawyers, convoluted inheritance schemes, menacing surveillance, comical and incompetent local police, porters and proctors, and so on. But it's great fun and I enjoyed it. Once or twice, characters step out of the book to converse with the author, which feels quite Eco-esque. Much of Oxford hasn't changed, though I do find it difficult to imagine a historical version of Cornmarket somehow. Like strange_complex's copy, the copyright is assigned to Jean Bell. Investigating on the Internet doesn't reveal much, although she is also acknowledged on a CD containing some of Montgomery's music (Crispin was a pen name) and in a biography, so presumably that itself involves some more or less convoluted inheritance.