"Prudence Hardcastle is on the pill. So is her sister-in-law, but someone has been swapping aspirin for their pills. Is it the teenage niece, the maid, the chauffeur, a lover, Prudence's husband Gerald, or all of the above?"
Deborah Kerr
as Prudence Hardcastle
David Niven
as Gerald Hardcastle
Robert Coote
as Henry Hardcastle
Irina Demick
as Elizabeth Brett
Joyce Redman
as Grace Hardcastle
Judy Geeson
as Geraldine Hardcastle
Keith Michell
as Dr. Alan Huart
Edith Evans
as Roberta Bates
David Dundas
as Tony Bates
Vickery Turner
as Rose
Hugh Armstrong
as Ted
Peter Butterworth
as Chemist
Moyra Fraser
as Woman in Tea Shop
Annette Kerr
as Gerald's Secretary
Harry Towb
as Racetrack Official
Jonathan Lynn
as Chemist's Assistant
Roy Beck
as Hospital Visitor (uncredited)
Ivor Dean
as City Banker in Taxi Cab (uncredited)
Arthur Hewlett
as Mr. Ferguson (uncredited)
Michael Hordern
as Dr. Morley (uncredited)
John Tatham
as Man Sitting in Grandstand at the Races (uncredited)
Joseph Tregonino
as Waiter (uncredited)
Fielder Cook
Director
Ronald Neame
Richard Williams
Opening Title Sequence
Katherine Haber
Producer's Assistant
Wilfred Shingleton
Production Design
Hugh Mills
Screenplay
Bernard Ebbinghouse
Music
Bert Ross
Sound Designer
Ronald J. Kahn
Producer
Fred Carter
Art Direction
Ted Moore
Director of Photography
Norman Savage
Editor
Julie Harris
Costume Design
Kenneth Harper
John Jarvis
Set Decoration
Tony Sforzini
Makeup Artist
Gordon K. McCallum
Sound Mixer
Otto Snel
Sound Re-Recording Mixer
Novel
Ted Sturgis
Assistant Director