A female hiker finds a dead woman on the North York Moors in England. The strangled victim is identified as Alice Ruber. Four months later, an insurance company asks detective Hercule Poirot to examine an expensive diamond belonging to millionaire Sir Horace Blatt.
Peter Ustinov as Hercule Poirot Maggie Smith as Daphne Castle Colin Blakely as Sir Horace Blatt Diana Rigg as Arlena Stuart Marshall Denis Quilley as Kenneth Marshall, Arlena's husband Emily Hone as Linda Marshall Roddy McDowall as Rex Brewster James Mason as Odell Gardener Sylvia Miles as Myra Gardener Nicholas Clay and Jane Birkin as Patrick and Christine Redfern John Alderson as Police Sergeant Paul Antrim as Police Inspector Cyril Conway as Police Surgeon Barbara Hicks as Flewitt's Secretary Richard Vernon as Flewitt Robert Dorning as Concierge Dimitri Andreas as Gino Walter Henry as Waiter Eric Kent as Desk Sergeant Guy Standeven as Vicar On Train
