Deanna Durbin stars in Lady on a Train, a murder-mystery with a delicious comedic twist. A young woman (Durbin) on a New York-bound train is witness to a murder outside her compartment window. With a penchant for reading mystery novels and the help of a mystery writer (David Bruce), she sets out to solve the case after police refuse to believe her story. The plot thickens when she is caught at the victim's estate and mistaken for his showgirl fiancee. Adopting the ruse, she soon discovers that, much to the chagrin of the family, the deceased has willed her most of his vast fortune!