Masked bandit The Lincoln Highwayman terrorizes motorists on California highways. His latest victims are a San Francisco banker and his family on their way to a party. While the masked highwayman holds them up at gun point and steals the women's jewels, the banker's daughter Marian (Lois Lee) finds herself strangely attracted to him. When the family finally arrives at the party, they tell the guests their tale. Secret Serviceman Steele takes an interest in their encounter and starts working on the case. Jimmy Clunder (William Russell) arrives late and while talking to Marian a locket falls out of his pocket. Marian recognizes it, but Clunder claims that he found it on the Lincoln Highway. She begins to suspect that he is the Lincoln Highwayman, as does Steele, Clunder's rival for Marian's love.