When Jimmy Wakely's pal "Cannonball" receives a letter from a former girl friend, Martha Fennamore, inviting him to visit her, Jimmy goes along to keep him out of trouble. Meanwhile, the widowed Mrs. Fennamore has discovered that the water in the reservoir near her ranch has been polluted. Schoolteacher Judson has been hauling in water for her but is actually in cahoots with Turner, a crooked land developer, who is trying to force Mrs. Fennamore off her ranch by poisoning the reservoir. Before he can get to her ranch, John Colton, the engineer whom Mrs. Fennamore has hired to report on the condition of the water, is killed by Smoky, one of Turner's henchmen. Upon arriving in town, Jimmy meets Mrs. Fennamore's niece, who is also named Martha, and assumes she is Cannonball's friend. After Jimmy serenades her on Cannonball's behalf, she socks Cannonball. Cannonball is rescued by Mrs. Fennamore but is then eager to avoid any involvement with her. Turner, meanwhile, hires a gunman, Easy, to impersonate Colton and give a false report on the water situation in order to force Mrs. Fennamore and others to sell their land. At a special town council meeting, Easy states that the water cannot be improved and advises everybody to leave. However, Jimmy challenges Easy's report and suggests further deep water tests. After Easy starts a fistfight with Jimmy, Mrs. Fennamore decides to authorize a deep water test. Her niece, however, decides to return to St. Louis and is persuaded by Judson to sell land she owns nearby, which has the only good water. This sale causes dissension among the remaining residents. Later, Jimmy proves that the water below the surface is free of contamination and after accusing Easy of being an impostor, holds him prisoner until he can get responses to some wires he sends. Judson learns where Cannonball is guarding Easy, slugs Cannonball and kills Easy. Jimmy, however, wraps Cannonball's face in bandages to impersonate Easy, whom he announces is still alive, hoping that Judson and Turner will give themselves away when they again try to silence Easy. Although Jimmy is caught eavesdropping outside Turner's office, he escapes and arrives in time to stop Judson from killing Cannonball. After the sheriff arrests Judson and Turner, the water in the reservoir is cleaned up. Jimmy then rides off with Cannonball, who is very unwilling to settle down with Mrs. Fennamore, who runs after him.