American secretary Karen Williams travels to Italy with her employer, art appraiser Raymond Fountaine, to assess the valuable collection of Count Paolo Barbarelli at his villa overlooking the sea.

The count lives there with Cora, a young woman suffering from memory loss, whom he claims to have taken in like a daughter after her skiing accident.

He is slowly poisoning her so he ultimately can inherit her family's money, Cora says, but Karen isn't sure whether to believe her story.

The police believe it to be a suicide, but evidence at the scene leads Karen to believe that Paolo was indeed responsible for the young woman's death.

A vicious watchdog tries to protect his master, but instead knocks Paolo into a fountain, where he drowns.