Mrs. Smith receives an anonymous letter stating that her husband is untrue to her, and she calls upon the detectives to shadow him. Smith comes home and, finding his wife away, goes out to look for her, in his shirt sleeves. Mrs. Smith points him out to the detectives, and they start on his trail. In the meantime Larkins, a police captain, is at home with his wife, and goes out to buy some ice cream, also in his shirt sleeves. As Smith enters a house Larkin comes out, just as the detectives turn the corner, and they, thinking Larkin is Smith, follow him. When Larkin returns home his fond wife makes much of him, all of which is noted by the detectives at the window. They finally decide to arrest him, and a furious scene is raised by the indignant Larkin and his wife, but to no avail, for Larkin is dragged off. In the meantime they have notified Mrs. Smith and she is on the way to meet them with three policemen, and Smith himself comes up at the same time. When Larkin and Smith get through with the detectives they have learned the painful lesson that it does not pay for a detective to make a mistake.