Foreign agents are smuggling monium (a chemical used in producing poison gas) into Mexico. The three Mesquiteers get involved when they ride to save a girl (really a government agent) on a runaway horse.

Returning a lost item to Ann, Stony arrives just two men shoot each other. Ann is a Government Agent and she gets Stony to replace her now dead partner. An important chemical is being smuggled out of the country and she sends Stony to the storage facility posing as the foreign Agent. He fools the guards but the boss arrives to expose the hoax and Stony is made a prisoner.—Maurice VanAuken <[email protected]>