六人在马赛乘坐火车到巴黎。 到达后，却发现一名妇女死于车上。 警方随即调查了另外五名乘客，并怀疑其中一人是凶手，但嫌疑犯一一离奇死亡。 最后两个幸存者必须在自己成为下一个受害者之前靠自己调查清楚。

A Parisian museum director believes his wife has lost interest in him and so places a poisoned cigarette in the box on his desk - thus allowing chance to decide the moment of his death.