Clem Maitland, a rookie cop, travels his beat accompanied by his police dog, Ace, until the police commissioner, ridiculed by the press because of the department's inability to curb the current crime wave, bans the canine. The commissioner's animosity toward the dog intensifies when Clem's friend, Tom Hadley, is accused by an eyewitness of robbing a fur warehouse, and the dog disputes the identification. Consequently, when the crime ring decoys Clem while he is guarding a payroll truck, and makes a clean getaway with the money, the commissioner suspends Clem from the force. Undaunted, Clem and Ace investigate the scene of the crime and discover a glove that one of the thieves has left behind. Realizing that this evidence presents the one chance to clear his friend, Clem and Ace trace the glove's owner to the roadhouse that serves as the gang's headquarters. That night, Clem, accompanied by his fiancée, Gerry Lane, the police chief's daughter, goes to the roadhouse to investigate. Recognizing Clem and his dog, the crooks take them prisoner along with Gerry. However, Ace makes a daring escape and frees Clem, who calls the police for reinforcements. As the police converge upon the roadhouse, Ace fingers the ring leader. The canine's heroics put an end to the commissioner's prejudices, as he officially authorizes the use of dogs in police work.