Tom Murray's wedding day takes a turn for the worse when a mysterious woman arrives uninvited and claims to be his wife.

A composer (Laurence Payne) is stuck in a middle-class marriage and finds that his affair with his wife's half-sister (Jane Griffiths) has resulted in a pregnancy. When his wife refuses to give him a divorce he hatches a murder scheme that is too clever by half.

There's pandemonium in a country house when various relatives come to stay.