A wealthy man murders his wife in their Italian villa by poisoning her milk and asphyxiating her with gas, then hides in a trapdoor until the body is discovered. His stepdaughter suspects him, as she had accused him of killing her father years prior, but her claims are ignored. The killer also poisons their family dog when it becomes too curious about his disguise.
The Snorkel
A teenage girl's mother is found dead, with the police ruling her death a suicide. However, the girl is convinced that her stepfather is responsible for her mother's murder.