When asked by the police commissioner why his dog Tarzan should receive a police honor medal, Lloyd Wilson, an assistant cashier, relates the following story: While Lloyd arranges with bank president Ernest Seaton to pick up $200,000 in bonds for immediate delivery to his company, Bert Doran, a new bank depositer who has been recruited by Ernest's daughter Ann, Lloyd's fiancée, listens with interest to their conversation. Through a coded message, Doran, who is actually the head of a small criminal gang, contacts his henchmen, Blackie and Gertie, and orders them to steal the bonds from Lloyd's office. Before Blackie and an accomplice can open the office safe, they are interrupted by the unexpected arrival of Lloyd. With help from Tarzan, who has been watching the burglary through a window, Lloyd tries to stop the robbers but finally is overwhelmed and knocked out. Although Lloyd immediately notifies the police of the theft, Surety, the company that was to receive the bonds, insinuates through the newspapers that the robbery was an "inside job" perpetrated by Lloyd. Ann and her father believe in Lloyd's innocence, but he is determined to clear his name by finding the stolen bonds himself. He is hampered in his efforts, however, by two private detectives who have been hired by Surety to trail him. At a swimming party at Ann's home, Tarzan conveys to Lloyd his intense dislike of Doran, who is a rival for Ann's attentions, and Lloyd becomes convinced that Doran is a suspicious character. Later, outside Lloyd's office, Tarzan spies Blackie and Gertie and jumps on the back of their car, riding with them to Doran's house, where they try to steal the bonds from a safe. After witnessing Doran confront and threaten the double-crossing Blackie and Gertie, Tarzan sneaks away with the empty bond satchel and returns to Lloyd's office with it. The satchel convinces the police, who are just about to arrest Lloyd, to follow Tarzan back to Doran's house. After a fierce fight involving Lloyd, Tarzan, the police and the robbers, the bonds are recovered and Lloyd is vindicated. Lloyd then concludes his story of Tarzan's bravery, and Tarzan is awarded his medal.