During a visit to childhood friend Edith, retired housewife Hetty Wainthropp discovers that Edith's husband, Frank, has a son by a previous marriage. Hetty decides to turn amateur detective to trace him. When this gives her a taste for detection, Hetty decides to set up a private detective agency.

Patricia Routledge
as Hetty Wainthrop

Tony Melody
as Robert Wainthrop

Jimmy Jewel
as Frank Cross

Jean Heywood
as Edith Cross

Gary Waldhorn
as Bernard Shawcrose

Gary Halliday
as Geoffrey Shawcross

Ram John Holder
as Chalky White

Jean Kent
as Phillida Meadowhite

Janet Allen
as Mrs. Lilium

Andrew Paul
as Photographer