A young man employed at a moving picture theater is studying to be a detective by reading a book. Although he wants to buy the girl he loves a large box of chocolates, he is one dollar short of cash. While sweeping the entrance of the theater, he unexpectedly finds a dollar bill in a pile of trash, but when a female customer arrives to inquire about money she lost, the young man gives her the bill he found. Then, when a tearful older woman also claims to have lost a dollar, he gives her one from his own pocket. Next, he is so intimidated when a burly man begins looking through the trash, that he hastily offers him his own dollar. However, the tough man returns the money, then reaches into the trash to retrieve a wallet stuffed with bills. Resigned to his lack of funds, the young man settles for the least expensive chocolates and, soon after, in the parlor of her father’s house, he shyly gives the girl the candy as well as a ring with a tiny diamond. Unnoticed by them, the “local sheik,” a rival for the girl’s affection, enters the house and steals her father’s watch and chain from a vest hanging on a coat rack. He then sells it at a pawnshop for four dollars and uses the money, to buy the largest box of chocolates, which he presents to the girl. When the girl’s father reports that his watch is missing, the young man consults his book to see what a detective should do. His distraction provides the rival an opportunity to slip the pawnshop receipt into the innocent young man’s pocket. Following the book’s advice, the young man searches everyone in the room, including the father’s hired man, and is surprised when the receipt is found on himself. The father banishes the young man from the house, and the disappointed girl returns his ring. When the local sheik leaves, the dishonored young man “shadows” him in the manner his book instructs, following him through the city into a freight yard, where his rival locks him in a box car and gets away. Although the young man escapes the moving train by grabbing the spout on a water tower, he is soaked to the skin and feels like a failure. Feeling dejected, he returns to the theater and sets up the projector for the next show, unaware that the girl has meanwhile learned from the pawn shop owner the true identity of the man who stole the watch. While waiting for the next reel of the evening's film, Hearts & Pearls or The Lounge Lizard's Lost Love , to change, the young man falls asleep and dreams that the girl, her father and his rival become characters in the film. In his dream, the young man leaves behind his body and the projection booth, crosses through the theater audience and enters into the film, where he has many cinematic adventures before becoming “the world’s greatest detective--Sherlock Jr.” In the film, the girl lives in a mansion with her wealthy father. Neither are aware that the young man’s rival has stolen a pearl necklace from the family vault with the help of the hired man, who serves as a butler in the film's elegant surroundings. Upon learning that Sherlock has been summoned to solve the crime, the thieves set traps in the billiard room, hoping to fell the master detective with either a decorative medieval axe that has been rigged to fall off the wall onto him or with a billiard ball, number 13, that contains explosives. When Sherlock the “crime-crushing criminologist,” arrives, dressed in an elegant coat and top hat, he closely observes the people in the room, and evades the falling axe and the offer of a poisoned drink. When he begins to play pool, the thieves wait for the explosion, which never happens, and are unaware that Sherlock has discovered and taken possession of the dangerous billiard ball. The next day, Sherlock’s valet, Gillette, helps him prepare for the day, then Sherlock joins the action that awaits him on the street. Sherlock follows his rival to the roof of a building, then jumps into the back seat of the car his rival is driving. He is there when his rival takes the pearls to a gang of outlaws, who nab the detective and threaten to kill him. When Sherlock learns that the girl has been abducted and taken to a cabin, he escapes with the pearls and disguises himself as an old woman, with the help of Gillette. Although the thugs pursue him, Sherlock uses many clever tricks to avoid capture, then jumps onto the handlebars of a speeding motocycle driven by Gillette. Although Gillette falls off the cycle when it bumps over a large rut in the road, Sherlock continues rolling unscathed through many dangerous situations, unaware that he is alone. He discovers his predicament just before rolling into the cabin where the girl is being held, but then is able to drive off with her in one of the outlaws’ cars. Although the outlaws are in close pursuit, Sherlock gets rid of them by throwing the explosive billiard ball, but then is unable to brake the car before it careens into a lake. Undeterred, Sherlock fashions a sail out of its convertible roof, enabling the couple to remain afloat for a while. He returns the pearls to the girl just before the car begins to sink. Awakened, the young man is back in the projection booth and still feeling the sting of failure, when the girl arrives with an apology from her father. Taking his cue from the movie that is still playing on the screen, he takes her hands and kisses them, places his ring on her finger, then kisses her. When he checks the film for further instructions, he is bewildered to see that the couple on the screen now have two babies.