In the sleepy English village of Sanford Angelorum, professor and amateur detective Gervase Fen is taking a break from his books to run for Parliament. At first glance, the village he's come to canvass appears perfectly peaceful, but Fen soon discovers that appearances can be deceptive: someone in the village has discovered a dark secret and is using it for blackmail. Anyone who comes close to uncovering the blackmailer's identity is swiftly dispatched.

As the joys of politics wear off, Fen sets his mind to the mystery but finds himself caught up in a tangled tale of eccentric psychiatrists, escaped lunatics, beautiful women and lost heirs.