His father, played by Michael Duchaussoy, starts to write a diary, which makes it clear that he is determined to track down the driver of the car, and take murderous revenge. The police fail to find the culprit, but a lucky chance puts the father on the right trail. He establishes that the driver was a businessman who owns a garage, and that he was accompanied by a young actress with whom he had had a fling.
The father begins a relationship with the actress, and she introduces him to the garage owner and his family. Almost everyone hates the garage owner, a selfish bully with few redeeming features, but when the father has the chance to kill the man he's pursuing so relentlessly, he does not take it. Nevertheless, in due course, justice is done – but who is responsible? The ending is ambiguous.
I enjoyed the film, and I enjoyed the book on which it is based – The Beast Must Die, by Nicholas Blake – when I read it a couple of years ago. But the two are very different. Blake's novel has a clever twist absent from the movie version, and features his regular series detective, Nigel Strangeways, whereas the film focuses on psychological suspense rather than mystification. Both book and film are, however, highly accomplished and have stood the test of time.