Poirot's Christmas is interrupted by Simeon Lee, who believes his life is threatened. Simeon is soon killed and his diamonds stolen.

Poirot and Hastings are at Lake Windermere for an attempt on the world speed-boat record. An elderly widow is hurt by falling down stairs, then later killed by poisoning with phosphorus.

Poirot and Hastings are on holiday in Deauville and receive a visit from Paul Renauld, who believes he's being cheated by Chileans. Renauld is kidnapped and his body is later found buried in a new golf bunker. French detective Giraud unwisely challenges Poirot to catch the killer before he can.

A string of thefts at a student hostel run by Miss Lemon's sister ends in death and Poirot has a number of plots and sub-plots to untangle. A certain mouse is the only witness to a string of murders.