In a prologue, the evolution of banditry from the road agent to the modern automobile bandit is depicted. In the main story, Marian Calvert, traveling along the California coast with her uncle and his family to a weekend party, becomes infatuated with the infamous Lincoln Highwayman when he robs them of their jewelry and leaves in his high powered auto. At the party, when late arrival Jimmy Clunder drops one of the stolen jewels, Marian's suspicions are aroused even though he explains he found it on the road. Steele, a secret service man at the party, who is in love with Marian, vows to capture the criminal, while the Governor of California appoints Captain Claver from the Sacramento police and his assistant to catch him. When Jimmy, with the help of his very intelligent dog Spike, holds up Steele and Marian to prove Steele's incompetence, Marian, convinced that Jimmy is the thief, falls more in love with him.