When a ransom bid results in the death of a child, the police have only one lead – the old lady who witnessed the kidnapper using a public phone box. Though her recollection is vague, she volunteers to act as bait for the killer – telling the press that she had seen the kidnapper's face and she waits for him to attack.

Meet Ellen Sheppard, an American living in Britain. Her English husband, Jason Sheppard, has been killed and she's under suspicion despite the appearance of a happy marriage. Jason's friend assists Ellen go over the facts to see if they can find the real killer.