A movie projectionist wants to be a detective. After being accused of stealing a watch, he projects himself into the movie and tries to solve a similar crime.
Sherlock Jr. (Buster Keaton) studies how to be a detective and is told to clean up the movie theater. Sweeping the trash, he finds $3. A woman says she lost a dollar, and he gives her one. Then another woman says the same and gets a dollar. Sherlock asks a man if he lost a dollar; he says no, but he searches and finds much money.
Sherlock spends a dollar on a gift for the girl (Kathryn McGuire) and changes the one dollar price to four. The villain (Ward Crane) takes a watch from a coat in the hall. Sherlock gives the girl a ring. The villain pawns the watch and buys the girl a present. Her father (Joe Keaton) says his watch was stolen. Sherlock consults his book and searches everyone. The father finds the $4 pawn ticket in Sherlock's pocket and tells him never to come back. The girl cries.
Sherlock follows the villain closely. He is locked in a railroad car and gets drenched by a water tank. Sherlock goes to work and shows a film. The girl asks the pawnbroker about the watch, and he points out the villain.
While Sherlock's body sleeps, his spirit walks into the movie. He appears in various scenes. A man says pearls were stolen, and the villain hands them to the butler (Erwin Connelly). Detective Sherlock comes in and looks into their eyes. The butler poisons wine, but Sherlock hands it to the villain. The butler puts an explosive ball on the pool table and leaves the room as Sherlock plays pool and keeps missing the explosive ball. The butler drinks the poisoned wine.
Sherlock follows the villain but gets stuck on a roof. He grabs a railroad crossing bar and comes down with it into a car. The villain and his gang capture Sherlock. The villain says he will torture Sherlock and that the butler has abducted the girl. The villain shows him the pearls, and Sherlock escapes. They chase him, and he seems to disappear into a woman. A motorcycle cop tells Sherlock that he is running too fast. Sherlock sits on the handlebars, but the cop falls off. Sherlock coasts through traffic and disrupts a picnic. He has numerous narrow escapes and then realizes he is alone. He runs into the butler and escapes with the girl in the gang's car. They chase them in another car. Sherlock drives the car into a lake and puts up a sail, but the car slowly sinks.
Sherlock wakes up in the projection booth. The girl comes in and says her father made a mistake. Sherlock watches the movie and imitates kissing her hands, giving her a ring, and kissing her. When the movie shows the couple with two babies, he scratches his head.
This fast-paced comedy lets the audience join the fantasy
of the employee who longs for a more interesting life like those
in the movies. He dreams of being a detective and confuses his
dream with movies, which are so much like dreams.