Just as Judge Ames is swearing in Barney Regan as the new city marshal, a gang of outlaws under the secret leadership of crooked lawyer John Wagner robs the Centerville bank. Barney and his deputy, Skipper Horton, give chase and bring back one of the wounded outlaws to Barney's young physician friend, Dr. Tom Creighton. Tom, hard up for the money he needs to buy needed equipment and to marry his sweetheart, Betty Ames, agrees when Wagner offers him a new microscope in exchange for keeping the prisoner from being questioned until the next day. That night, Wagner sends his henchman "Pills" Fowler to murder the wounded man. Tom goes to Judge Ames and voices his suspicions of Wagner, but Wagner sends "Pills" on another mission and the Judge is found dead with one of Tom's scalpels driven through his heart. Barney and Skipper set out to clear Tom, and are aided greatly by the fact that "Pills" is a confirmed hypochondriac.