Evil Under the Sun

A hiker finds a dead woman on the Yorkshire moors; the victim, who has been strangled, is identified as Alice Ruber. Shortly afterwards, Belgian detective Hercule Poirot examines a diamond belonging to millionaire industrialist Sir Horace Blatt (Colin Blakely) and declares it a fake. Arlena Stuart Marshall (Diana Rigg) is on holiday with her husband Kenneth (Denis Quilley) and flirts with Patrick Redfern (Nicholas Clay), who is himself married to the meek meek Christine (Jane Birkin)