An Australian nurse discovers an effective new treatment for infantile paralysis, but experiences great difficulty in convincing doctors of the validity of her claims.

Talbot uses a phony land grant to rule thirteen million acres, taxing everyone heavily and evicting those who won't pay. The Three Mesquiteers becomes mysterious "night riders" to fight this evil.

Truck drivers Steve Hackett and Bill Purvis are fired from their jobs with the West Coast Trucking company for not using second-gear going down steep grades. Davis, the company vice-president, surprisingly asks them to carry a load of merchandise to Arrowhead and offers a $1000 bonus. He tells them it is a load of lettuce. Several miles out of Los Angelese, they are stopped by a mob of lettuce-farm workers on strike. When the first crate is tossed off the truck, it explodes and the two pals learn their merchandise is a cargo of dynamite. The workers let them proceed and they crash into a car driven by Mary Stevens, whom they had met at a restaurant. She and her dog, "Butch" (played by a Credited dog named Stooge), join them and they deliver their cargo, and learn unscrupulous real-estate operators have jammed the locks on the dam in order to ruin the ranchers and farmers and take over their property.