 The fifth of the Hopalong Cassidy films and the first to establish Cassidy (William Boyd), Johnny Nelson (Jimmy Ellison) and Windy Halliday (George Hayes) as a continuing Bar 20 trio (hence the title), although the Windy character was a film creation and never one of the characters in the Clarence E. Mulford books. This one finds the town of Mesquite in the grip of Pecos Kane (Onslow Stevens), suave, cultured gambler, who, unknown to his fellow citizens, is the leader of the band of rustling and robbing desperadoes. Angered by Johnny s friendship with the new school mar m, Mary Stevens (Muriel Evans), Kane tries to frame Johnny, along with Cassidy, on the charge of robbing the stagecoach and killing the driver. This fails, but Kane s gang takes Cassidy and Johnny prisoners, and to their desert hideout. The two make an escape and return to Mesquite, where they manage to convince the townspeople of Kane s trye nature. Kane, with Marty as his prisoner,and his henchmen barricade the saloon, which is soon afire. Hoppy is wounded, but Johnny, Windy and the others make their way into the saloon, killing Kane and his henchmen and rescuing Mary.