U. S. marshal Lash LaRue and his partner Fuzzy Q. Jones are passing through a small town when gunshots are heard at the saloon. Lash and Fuzzy enter the saloon, where a drunken man named Matt is recklessly firing his gun. After Lash shoots the gun from out of Matt's hand, he knocks him out in a fistfight. Saloon patron Walker then compliments Lash on subduing the drunken Matt, after which Lash and Fuzzy check into the local hotel. Late that night, as Fuzzy complains to Lash about his toothache, Walker knocks on the door. Walker reveals that he is a Pinkerton detective and states that he recognizes Lash as a U.S. marshal. He then proposes that Lash join forces with him to apprehend some local outlaws. After explaining that the Taggert and Jackson gang are running a "tin-can telegraph," a relay system using coded messages, Walker asks the lawmen to intercept a message, hoping that it will detail the next robbery the gang plans to commit. Walker continues that because the gang recently killed his partner, he needs Lash and Fuzzy's help to solve the case. When Walker offers half of the reward money for apprehending the gang to Lash and Fuzzy, they accept to the job. The next day, Lash and Fuzzy spot a suspicious rider near the area Walker asked them to patrol. Lash leaves Fuzzy, who is tending to his toothache, and follows the rider to a shack. After the rider leaves, Lash whips the gun from the hand of a gang member guarding the shack and knocks him out. He then searches the cabin, finds the message and memorizes the code. After the outlaw gang discovers that Lash attacked and has possibly intercepted their message, outlaw chief Lou orders his henchmen, Horn, Rocky, Bart and Larson, decide to kill Lash and Fuzzy. When the henchmen attempt to ambush Lash and Fuzzy on the trail, Lash engages two men in a fistfight while Fuzzy subdues another and lassos their last pursuer. After Fuzzy is dragged behind the lassoed man's horse, Lash rushes to his rescue. With one shot, Lash scares the outlaw away and then allows the others to flee, hoping that they will lead him to more clues about the case. Later, Lash and Fuzzy meet with Walker, who deciphers the message and learns that Taggert and Jackson are planning to meet that night in Fall River. Lash, who has a personal vendetta against Jackson for killing one of Lash's friends, offers to go to Stark City to alert Pinkerton detective Denton, who is in charge of the area near Fall River. In Stark City, Lash becomes suspicious of the lack of activity in town and sends Fuzzy to guard the back of Denton's office. As Lash approaches the office, two men attack him. After subduing his assailants, Lash delivers the message to Denton. Meanwhile Denton's detectives, including Matt, who is secretly in league with Taggert, have arrested and identified Lash's attackers as Taggert's men. Denton then explains that Taggert and Jackson use Stark City as a pickup point. Denton, who is shorthanded because he has stationed his men through the area, asks Lash to take general store owner Kimberly and young Danny Bryan to detain Taggert and Jackson in Fall River, while he gathers the rest of his men to meet Lash there later. Later, Matt warns Taggert and Jackson that Lash on his way. That night when Lash, Fuzzy, Kimberly and Danny arrive in Fall River, Taggert's men are positioned throughout the town, which is otherwise abandoned. When a shootout ensues, Lash orders his men to take cover. Fuzzy then uses his "old Indian trick": putting his hat atop his gun, he lures a gunman on a nearby roof into view after which Lash shoots the outlaw. While Lash, Fuzzy and Kimberly cover him, Danny runs to the general store, where one of the gang wounds him. After Lash exchanges gunfire with the outlaws, Jackson catches him off guard and holds him at gunpoint, but Fuzzy appears just in time to get the drop on Jackson. Not satisfied with just arresting Jackson, Lash challenges him to a shootout, in which he kills the outlaw. To capture Taggert, Lash writes a note, ordering Taggert to surrender by 10:00 am the next morning and gives it to Fuzzy to deliver to Taggert's office in the local saloon. When Taggert fails to appear the following morning, Lash goes to the saloon and tricks Taggert into firing all his ammunition by swinging the saloon doors, which indicates that Lash is outside the saloon. Taggert then flees on horseback with Lash in pursuit. Using his whip, Lash pulls Taggert from his horse, after which they begin a fight. Lash easily triumphs and then arrests Taggert. After the townspeople congratulate Lash, Fuzzy, Kimberly and the wounded Danny, Fuzzy complains about his tooth again. When Lash orders him to see a dentist, Fuzzy turns to leave the saloon. To everyone's entertainment, the door hits Fuzzy's face, loosening his tooth, which then he pulls out, happily surprised.
