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.