Set in Italy in an ornate villa, you see the crime from the beginning, and how it is pulled off in detail. An apparently fortune hunting husband, Paul Decker (Peter van Eyck), has put a powerful sedative in his wealthy wife's drink causing her to fall into a deep sleep, has taped up the windows, locked the doors to the room she is in, and turns on the gas in the room. He dons a snorkel connected to air coming from outside and stays in the room until the next morning when the servants arrive. He then hides in a section under the floor, with the opening to this compartment hidden by a throw rug. The servants find their dead mistress, call the police, and the woman's death is ruled a suicide. The murdering husband slips out and leaves after everybody has left the villa.

The dead woman's daughter, Candy, about 13, is not buying it. She says she saw the man kill her father - his death was ruled an accident - and says that her mother had no reason to kill herself, especially on the day she was returning home from boarding school. But nobody believes her and her stepfather has a passport stamped by the Italian authorities saying he came back to Italy from France the day after his wife died.

So the rest of the film is a tense cat and mouse game between Candy and her stepfather, with her trying to figure out how he did what he did, and with nobody believing her, and her stepdad doing a good job of playing the grieving husband. He charms the close family friend caring for Candy, and the police seem determined to close the case and call this a suicide because, after all, for the husband to have done it he would have had to be in the locked room the entire time that the gas was on AND live. Of course, the answer is in the movie title, and somehow I think Columbo would have had a harder look at the stepfather than the police did here. In fact, this is set up very much like an episode of Columbo - you see the crime, you see the criminal, but Columbo has to prove what he suspects going initially only on a hunch.

There is a terrific twist at the end and is well worth sticking around to see. Let's just say the ending is heavy.