Hercule Poirot is admiring the Sacré-Coeur Basilica in Paris. On the flight from France to England while Poirot was asleep an old lady has been killed. It seems a poisoned dart was used.
Among the suspects is a crime writer and a snooty aristocrat, who was in Paris to see Fred Perry at the French Open and gamble. It seems she was in debt to the old lady.
Poirot and Japp visit Paris to find out more about the victim and seek out a woman who claims to be the victim's long lost daughter.
This feature length mystery has wonderful production values of vintage Paris and the recreation of the French Open. However it is padded more than a psychiatric cell. I know we have moved on from the Agatha short stories but really you can see the director falling back on various tricks just to drag the story out such as the scenes on the plane which go on for ages. We even have a character telling Poirot to get on with it during the denouement.