During World War I, a professional thief known as The Lone Wolf is assigned to steal a cylinder with important information from behind the German lines and bring it to Allied intelligence headquarters. However, German agents set out to stop him, headed by the man who was responsible for the death of the thief's sister.

Shortly after the engagement of John Brown and Hope Avery is announced, he receives an offer of a fine position in South America. She demurs at his going, but he overcomes her objections and after a tender farewell, leaves her with the promise to return within a year and make her his wife. Philip Lane is injured in an auto accident near the Avery home, and Hope discovers him. She has him taken to her home and during his convalescence, he falls deeply in love with her.