At a café, along a lonely highway in a small town, truck driver Steve Reynolds celebrates his sweetheart Eileen Blair's birthday by giving her an engagement ring and drinking a toast. After Steve leaves the party to make a delivery, a drunken driver swerves into his path, forcing him to smash into McCabe's gas station in order to avoid a collision. Don Parker, a motorcycle policeman and Steve's rival for Eileen's affections, witnesses the crash and arrests Steve for drunk driving. When Steve is found guilty and his license revoked, his only recourse is to run his business from his desk. Jerry Mason, Steve's competitor, offers to buy his business, but although in debt, Steve refuses. One night, one of Steve's drivers falls ill and Steve decides to drive the truck himself. Forced by engine trouble to stop along the road, Steve climbs out of his cab and is assaulted by a mysterious assailant, who knocks him unconscious and then seizes control of the wheel. When Don pursues the truck for speeding, Steve's attacker backs into the officer and kills him. Just then, Steve regains consciousness and begins to struggle with the man, but he escapes, leaving behind a glove with a missing thumb. Wanted for Don's murder, Steve goes into hiding, disguising himself as a blind man. Suspecting that Jerry is involved in the crime, Steve follows him to a restaurant and discovers that Jerry is running a stolen car ring from his garage. Hurrying to the diner, Steve entrusts the glove to Eileen for safekeeping, but their conversation is overheard by waitress Mabel Sands. Steve then enlists Charlie Cook, his friend and mechanic, to secure a job at Jerry's garage and observe the operation. When Charlie reports that several stolen cars have been delivered to the garage, Steve suggests going to the police with the information, but Charlie convinces him that they should apprehend the thieves themselves. That night, Steve finds Jerry's dead body on the floor next to an empty safe in the garage. At that moment, a shadowy figure knocks Steve unconscious. Upon regaining consciousness, Steve discovers that Charlie has also been knocked out. Dissuaded by Charlie from giving himself up, Steve returns to the diner, defeated, and Eileen shows him the cache of diamonds that she found concealed in the thumb of the glove. When Tommy, Eileen's young son, recalls seeing Mabel call someone, Steve begins to suspect that Mabel is in league with the glove's owner. Hurrying to Charlie's apartment, Steve tells Charlie that Mabel's boyfriend killed Don and Jerry, and asks him to accompany him to Mabel's apartment. Once there, Charlie trains a gun on Steve and declares that he is Mabel's accomplice. After explaining that he killed Don because the officer was blackmailing him about stealing the diamonds, Charlie forces Steve to write a letter to Eileen, claiming that the killers have captured him and Charlie, and are holding Steve hostage for the diamonds while Charlie delivers the letter. At the bottom of the page, Steve cleverly inserts a message stating that the diamonds are hidden in the glove, thus alerting Eileen to danger. Charlie then delivers the letter, and when Eileen and Tommy read it, they realize that something is amiss. After Eileen insists on driving Charlie and the glove to the criminals' hideout, Tommy notifies the police about his mother's license plate number. Tracing the car to Mabel's apartment, the police arrive just in time to arrest Mabel and Charlie as they are leaving the building. Exonerated of all guilt, Steve uses the reward money for the diamonds to rescue his failing business.