After his young wife Kate reminds him over the telephone that their second wedding anniversary is that day, Los Angeles accountant William Calhoun Denny rushes from the train station to a women's clothing store. He is followed there by a friendly Welsh terrier, who unknown to him, is the property of a gangster named "Short-wave" Bert. As Bill is about to purchase a nightgown for Kate, the dog accidentally breaks a window, and the salesclerk insists that Bill use all of his cash to pay for the damage. The dog then follows Bill home carrying the discarded "happy anniversary" tag in its mouth, and Kate thanks her husband for the wonderful present. Sure that his disapproving mother-in-law, in whose house the couple lives, will ridicule him for not buying his wife a gift, Bill does not correct Kate's mistake. When the dog, whom Kate names Archie, proves an impediment to Bill's lovemaking, however, Bill scours the classifieds and finds a listing for a lost dog whose description matches Archie's. Unknown to Bill, the ad has been placed by smuggler Pete the Pusher and his cohorts, Albert Jonas and Pinky, who have arranged to deliver contraband to Bert through the specially trained Archie. Moments after Bill telephones Jonas to tell him about Archie, another gangster, Gillie the Blade, slips in and stabs Jonas to death. Bill then shows up at the smugglers' address, but is dismissed by Gillie, who is posing as Jonas. Before leaving, however, Bill gives Gillie his calling card, which Gillie leaves on Jonas' corpse after notifying the police of his murder. When Gillie informs his boss, Fat Fred, about Bill's visit, Fat Fred deduces that Archie is somehow connected to the smugglers, whose goods he hopes to hijack, and places a second "lost dog" ad in the paper. Later, a shocked Bill is questioned by irascible homicide detective O'Ryan about Jonas' murder, but insists that he merely gave the man his calling card while discussing a lost dog with him. Bill then sees Fat Fred's ad in the paper and, eager to end Archie's continuing romantic interference, walks him to Fat Fred's. Fat Fred, meanwhile, has read yet another ad about a lost terrier, placed by Pete's contact Numi, and doctors a dog to look like Archie so that he can check out the smugglers while pretending to return the animal. Soon after Fat Fred leaves his place, Pinky and Pete, responding to Fat Fred's ad, show up and kill Gillie. Bill then arrives with Archie and is terrified to discover a dead Gillie, who he still believes is Jonas. After a stressful night chasing a runaway Archie, Bill tries to tell a suspicious Kate the truth about the dog, but she refuses to listen. The next day, Bill again informs O'Ryan that Jonas has been murdered, and while O'Ryan surmises that Gillie killed Jonas, and one of Jonas' cohorts killed Gillie, he is uninterested in Bill's complicated dog story. When Bill notices the third ad in the paper and faints, however, O'Ryan sends his men to the ad's skid row address. There, the police discover not only Fat Fred's body, but Numi's as well. Kate, meanwhile, tries to walk Archie along Wilshire Boulevard, the street on which the dog has been trained to make his rendezvous. The waiting Max spies Kate, who is carrying a bag of dog bones and, assuming she is Pete's courier, grabs the bag and thrusts a valise in her hand before fleeing. Upon inspecting the bag later, Max and Bert are furious to discover only bones, but Kate and her mother are ecstatic because the valise is full of money. After a distraught Bill points out that the money is counterfeit, however, he and a disappointed Kate return it to O'Ryan, who refuses to believe that it is in any way connected to Archie. Although O'Ryan finally forces Bill to confess that he did not buy Archie as an anniversary gift, Kate still insists on keeping the dog. Bill is equally determined to rid himself of Archie, however, and leaves him at a pet store, then tells Kate that he ran away. When Kate innocently places an ad for Archie and offers a reward, the greedy pet store owner returns the dog. Bill quickly realizes that the gangsters will also be arriving, but cannot escape before the gun-wielding Max and Bert show up. As soon as Kate reveals that the money in the valise was counterfeit, Max, who thought the cash was genuine, accuses Bert of double-crossing him. The two gangsters then shoot and kill each other. Kate faints and Bill telephones the police, who pull up just as Pete and Pinky storm the Denny home looking for Archie. After Bill slugs Pete unconscious and tricks the dimwitted Pinky into falling out a window, O'Ryan and his men burst in and arrest Pete and Pinky. Later, Bill, now hailed as a hero, collects several $5,000 rewards for apprehending the smugglers and accepts Archie into his life. Having finally proven himself to his mother-in-law, Bill then carries Kate triumphantly into their bedroom.