When Lord Crowley sends for him, cynical inquiry agent Knighton Gaunt is more than happy to accept the simple assignment. All he must do is attend a séance and expose the spiritualist, Prudence Barnard, as a charlatan taking advantage of Crowley's mother.

Unfortunately, instead of proving Miss Barnard is a fraud, Gaunt is made to look like a fool when Crowley is murdered after the séance. Apparently, the attractive spiritualist is not the only guest who has mastered the art of sleight-of-hand. Whoever killed Crowley managed to poison his brandy without anyone noticing and to act with appropriate concern afterwards.

The terrified guests immediately close ranks against Miss Barnard and accuse her of the murder. She is the only stranger in the house, except for Gaunt, and she'd argued with Crowley the previous day. It sounds reasonable to everyone except Miss Barnard. And Gaunt.

Then the murderer strikes again, and Gaunt must use all of his skill to expose the truth before another member of their house party dies.