Paul Decker (Peter van Eyck) has devised an elaborate plan to kill his wife Madge. First he drugs her milk. While she is asleep he tapes up the windows and doors and turns on the gas. He hides himself in a compartment under the floorboards. He has already installed two pipes that lead to the outside and fresh air. He puts on a snorkel and attaches two rubber hoses from the snorkel to the pipes leading outside. Underneath the floorboards he can safely remain indefinitely.

In the morning the servants find Madge’s body in the sealed room. They call the police. The Inspector (Gregoire Aslan) arrives at Decker’s villa along with the British Consulate Mr. Wilson (William Franklyn). Everything appears to point to suicide. Locked doors and windows, victim alone, no suicide note but they don’t always leave a note.

The same day Madge is found, her teenage daughter Candy Brown (Mandy Miller) arrives from school with her companion Jean Edwards (Betta St. John). Candy quickly accuses her step father Paul of killing her mother. She says he killed her father too years ago so he could marry her mother and get her money. All the while Paul is still under the floorboards listening. The only one aware that Paul is there is Candy’s dog Toto but no one is paying attention to the dog.

Jean takes Candy to the local hotel rather than stay in the villa. The next day Paul shows up at the hotel. He says he was in France and just got in. Candy of course accuses him of murder. No one pays attention to her but not taking chances Decker decides that Candy should go to America and stay with her aunt for awhile.

Candy believes that Decker was not in France like he said but was really in Italy. While Candy is snooping in Decker’s room for his passport Toto finds the snorkel in the wardrobe. Candy pays no attention to it. Decker catches Candy in his room he shows her the passport and proves there is no stamp showing he was in Italy instead of France. After Candy leaves his room Toto digs out the snorkel again. Decker decides that Toto has to go. He poisons the dog. Candy accuses Decker of killing Toto. She threatens him. She tells him he will have to kill her before she kills him.

A day at the beach is enlightening for Candy. She sees a man go into the water with a snorkel. Now she knows how Decker got to Italy from France without driving over the border. He swam. It's only a mile or so underwater. She also knows how someone can be in a locked room full of gas and still breathe air. Now she just needs to get someone to believe her before she is the next to die.

“The Snorkel” was released in 1958 and was directed by Guy Green. It is a British thriller produced by Hammer Films and was based on the novel by Anthony Dawson. The title may be a little strange for a thriller but the snorkel does play a prominent part in the film. The killer may be well known and so is the method of murder but the fun is in how he tries to stay unknown to everyone else despite being threatened by a Columbo-esque teenager. The ending is completely satisfying and wonderfully done.

Peter Van Eyck is great as the murderous sociopathic Decker who has no problem killing anyone in his way. Betta St. John as the companion/babysitter is a little annoying. Why she refuses to believe Candy even though she basically helped raise the child is beyond he. She herself knows there is something wrong with Decker when he makes a move on her but she is too quick to believe a creepy adult rather than the teenager she’s known all her life. Granted Candy didn’t have any proof but it seems strange that everyone in Decker’s life has a shortened life span. Candy herself wasn’t all that likeable either but I did love the way she acted at the end. If she has been any other way she would have messed herself up for life.

All together the film is good. Surprisingly, it’s a lesser known Hammer offering which is a shame.