Cast in order of appearance

Tredwell (the butler) Timothy Paul Evans
Lucia Amory (Richard's wife) Elizabeth Mander-Wilson
Miss Caroline Amory (Sir Claud's sister) Lizette Kent Allen
Richard Amory (his son) Steve Murdock
Barbara Amory (his niece) Jessica Seaman
Edward Raynor (his secretary) Terence J. Burke
Dr. Carelli (a visitor from Italy) Nicolás Peters
Sir Claud Amory (noted physicist) Bud Emerson
Hercule Poirot (Belgian detective) Michael Gardner
Captain Arthur Hastings, O.B.E. (Poirot's friend) Ivan Harrison
Dr. Graham, (local physician) Eric Hedberg
Inspector Japp (the police) Nick Reeves