On a French golf course, a millionaire is found stabbed in the back?

An urgent cry for help brings Poirot to France. But he arrives too late to save his client, whose brutally stabbed body now lies face downwards in a shallow grave on a golf course.

But why is the dead man wearing his son’s overcoat? And who was the impassioned loveletter in the pocket for? Before Poirot can answer these questions, the case is turned upside down by the discovery of a second, identically murdered corpse?