Due to the wartime manpower shortage, Dad Mathews cannot prevent rustlers from devastating his cattle herd. Dad attempts to hire any available man, but hands not in the military prove of little use. One day, state cattle commission investigators John Paul Revere and Frog Millhouse arrive at the Mathews ranch to find out why Dad has not begun fulfilling his contract for government beef. Dad explains the situation and Johnny and Frog immediately offer to help. Despite Johnny and Frog's efforts, the gang stages another raid, during which Dad recognizes a captured raider named Lefty Lewis and releases him without explanation. Lefty returns to the gang's headquaters, where the leader, Henry Judson, vows to continue the raids until Dad is forced out of business. Back at the ranch, Johnny is impressed by the riding skill of Dad's daughter Betty, and suggests that women be hired to work the ranch, as women have been successfully incorporated into other aspects of the war effort. Soon Betty organizes her friends into the Women's Army of the Plains and they begin patroling the ranch with walkie-talkies. Despite the reluctance of the young women's parents and the skepticism of some of the men, such as Frog, the "WAPS" handle themselves well and thwart another attack by the rustlers. The angry Judson orders Lefty and another henchman, Tex Coburn, to stop the women, whose parents gave them permission to operate solely on Johnny's promise that they would not be harmed. Lefty and Tex cause a number of accidents through sabotaging the WAPS's equipment, but the women do not reveal their injuries for fear of having their group disbanded. When Sally Meehan is hurt in front of her parents, however, Dad orders the women to leave their camp and return to the ranch. Johnny again captures Lefty, but while he is being questioned by Dad, Lefty identifies Dad as Dan Dowling, an outlaw convicted of murder twenty years earlier. Consequently, when word arrives that David Mathews, Dad's war hero son, is about to return home for a visit, Lefty orders Dad to release him or he will inform Betty and David about their father's criminal past. Meanwhile, Sally has convinced her parents to let her stay in the WAPS, and Johnny sends Frog to follow Lefty. In town, Frog overhears Lefty tell Judson that he committed the murder of which Dad was convicted, but Frog is captured by the gang before he can report to Johnny. Hearing that Dad has disbanded the WAPS, the rustlers stage another raid, in which they capture the remaining Mathews herd. Frog has managed to turn on his walkie-talkie and broadcasts the information to the women, who ride with Johnny and the ranch hands in search of the culprits. The ranchers finally find the gang's hideout, which is under a waterfall and through a tunnel, and Johnny saves Frog from an untimely death. Lefty is fatally wounded during the struggle, but before he dies, his conscience prompts him to remove suspicion from Dad by lying and saying that he is Dan Dowling, the wanted murderer. Later, everyone bids farewell to Johnny and Frog, and the WAPS present them with silver spurs.