 When his friend Tom Hadley is picked out of a lineup as one of the men who robbed furs from a warehouse, rookie cop Clem Maitland uses his police dog, Ace, to refute the eyewitness. Clem found a portion of ripped overalls at the scene, and Ace s keen sense of smell would have identified Hadley, he argued. But Police Commissioner Hugh Thomas, who doesn t believe in the usefulness of dogs in the police force, is not convinced, and Hadley is arrested. The next day, the same gang robs a payroll in broad daylight and kills the gateman after decoying Ace and Clem, who was assigned to protect the payroll. Despite being suspended, Clem tracks a glove left at the scene to one of the gang members, and takes his girl, Gerry Lane, and Ace to investigate the roadhouse being used as a front, unaware that he was spotted by the gang members, who lay in wait for them.