A woman witnesses a murder while looking out of a train window, and can identify the victim but not the killer. When the police dismiss her story, she turns to a writer of detective novels to help her investigate the crime and bring the elusive culprit to justice. Mystery, starring Deanna Durbin, David Bruce and Ralph Bellamy.

While watching from her train window, Nikki Collins witnesses a murder in a nearby building. When she alerts the police, they think she has read one too many mystery novels. She then enlists a popular mystery writer to help her solve the crime on her own, but her sleuthing attracts the attentions of suitors and killers.