When accident-prone street cleaner Red Jones proposes marriage to Ann Elliot, a secretary at the Fuller Brush company, she refuses his engagement ring and tells him that she will not marry him until he makes a success of himself. Ann also tells Red that he should be more like her friend Keenan Wallick, a successful Fuller Brush salesman. Later, Red accidentally causes a trash can fire and is dismissed from his job by Sanitation Commissioner Gordon Trist. To help Red find a new job, Ann arranges to have him tested as a door-to-door Fuller Brush salesman and teams him up with Keenan on one of his runs. Keenan, hoping to get Red out of his way so that he can pursue a romance with Ann, has the inexperienced salesman try out his technique on an "impossible" block. Red fails at his early attempts to sell the brushes, and Keenan, hoping to get rid of Red conclusively, makes a wager, using Ann as the prize, that Red will not be able to sell one single household on a brush. Red next attempts to sell brushes at the home of Commissioner Trist, but he is forcefully ejected from Trist's home when the commissioner realizes that Red is the man whom he fired. Mrs. Trist, however, buys ten brushes from Red. Later, while reporting his sales success to Ann and Keenan, Red realizes that in his excitement he forgot to collect Mrs. Trist's money. When he returns to the Trist estate, Red overhears the commissioner, his business partner, Gregory Cruckston, and others discussing their involvement in a war surplus racket. During the conversation, Sara Franzen, the fiancée of Gordon's son Freddie, tearfully confesses that she is in love with Gordon. Red is caught spying on the family from the garden, and moments after he is brought indoors, the lights go out and Gordon is found stabbed to death. As police lieutenant Quint searches the house for the murder weapon, all those present in the house, including Red, are arrested on suspicion of murder. Though the police initially believe Red to be the killer, he is eventually released for lack of evidence. When Red returns home, he finds Mrs. Trist waiting there. Chaos ensues when Ann arrives, followed by Freddie and two mysterious armed thugs. As the gunmen hold everyone in Red's apartment hostage and search the apartment looking for the murder weapon, Red and Ann discover that the weapon was one of the brushes from the Fuller Brush line, which had been melted and molded into a knife-like object. Before Red and Ann can take their theory to Quint, however, they are trapped by Cruckston, who reveals himself as the murderer. Ann and Red are taken prisoner by Cruckston and his cohorts, but they manage to escape to safety with the help of the police and firemen. With the murderer arrested, Red finally wins Ann's respect, and they embrace and kiss.