The Village Sleuth (1920)

William Wells is a country boy who graduates from a correspondence school as a detective. He gets his start by solving the mystery of disappearing watermelons from his father's patch. Then he applies for a job as house detective at a sanitarium, but instead ends up as the janitor. When a man is reported murdered, Wells suspects the man's wife. So he dons the dead man's clothes and visits the woman at night, hoping she will be scared into confessing. The dead man was short, fat, and wore a mustache; so Wells puts a pillow under his vest and puts on a fake mustache. When the woman sees him crouching in the shadows, she leaps out of bed, rushes toward him with her arms outstretched, and exclaims "My darling, so you are not dead!" Wells runs from the room. He falls for Pinky Wagner, who is accused of the murder. Wells manages to clear up the situation when he discovers that the "victim" has in fact not been murdered, but instead, a robbery had been committed.