In 1938, in English provincial life, a married couple the Faynes goes through difficult times. Their already less-than-ideal relationship is complicated by the wife’s suspicions that her husband might have killed his young mistress. After a meeting with her husband’s uncle, these suspicions only strengthen. At a dinner party with hosts and guests, a home hypnosis session is conducted. The spouses are the subjects, and during the experiment the wife, in a controlled trance, kills her husband with a knife that somehow replaced the rubber props. Local police, lacking sufficient experience, turn to Sir Henry, who planned to spend time away from city bustle working on his memoirs.