"Stony" Brooke, "Tucson" Smith and "Lullaby" Joslin, cowboys who are known as The Three Mesquiteers, greet their friend Jim Chapman, a telegraph engineer who has traveled West with his wife Alice and baby, little Stony, who is Stony's godson. Jim is in charge of building new telegraph lines from Fort Jackson to points throughout the West in an effort to increase communication and squelch a notorious gang. Tragedy strikes after the Mesquiteers leave Jim's party and the wagons are attacked by the gang. While Jim and his family are not hurt, the majority of his equipment and supplies is destroyed. Major R. C. Kelton, the commander of Fort Jackson, discounts Stony and Tucson's idea that with the aid of the telegraph, the troops would be better prepared and could stop such raids. Kelton and newspaper editor Jeff Bradley convince the town committee that no more money should be wasted on telegraph equipment, but Stony persuades Jim to install a trial line between Forts Jackson and Dodd to prove how useful it could be. Bradley, who is the secret head of the gang, prints a coded article in his paper, alerting his men to stage a raid on the construction camp. More equipment is ruined and Tucson and Stony become suspicious of Bradley, who has arranged for his henchman, Mason, to be Jim's guide. Stony and Tucson are arrested by soldiers when they fight with Bradley while trying to question him, but they escape from the guardhouse. Later, Mason sets up the construction workers, and they are all slaughtered by the gang. The only survivor is little Stony, whom Tucson and Stony take to Lullaby's cabin. The next day, the Mesquiteers are found by Kelton's daughter Marcia, who promises to care for the baby and promote their cause. She and Lullaby return to town, where she tricks her father into supporting the telegraph. Money is raised and soon a replacement engineer, Reynolds, is on the job despite the gang's attempt to steal the funds. While Reynolds builds the line to Fort Dodd and promises to connect the rest of the territory, Bradley plots his sabotage. With the aid of an ex-Army telegraph operator, Bradley sends a fake message from Fort Dodd that they are under attack. Kelton and the soldiers rush to the rescue, while Bradley and Mason head to the construction camp. Stony and Tucson, who had been captured and imprisoned by Kelton, escape and go with Lullaby to the camp. They try to hold off the gang but are outnumbered, and so Stony repairs the cut telegraph line and sends an emergency message to Fort Dodd. Kelton receives the message and races back to the camp. The cavalry arrives in time, and after the gang is apprehended, the communication system is finished. After Reynolds telegraphs a greeting to the governor with the aid of little Stony, Kelton thanks the Mesquiteers, who then leave for further adventures.