Crime author Dick Markham is in love again; his fiancée, Lesley Grant, the mysterious newcomer to the village. When Grant accidentally shoots a fortune teller through the side of his tent at the local fair - following a very strange reaction to his predictions - Markham is reluctantly brought into a scheme to expose his betrothed as a suspected serial husband-poisoner. That night the enigmatic fortune teller - and chief accuser - is found dead in an impossible locked-room setup, casting suspicion onto Grant and striking doubt into the heart of her lover. Lured by the scent of the impossible case, Dr Gideon Fell arrives from London to examine the perplexing evidence and match wits with a meticulous killer at large.