Frontier Pony Express is a 1939 American Western film directed by Joseph Kane and starring Roy Rogers, Lynne Roberts (as Mary Hart) and Noble Johnson as the lead villain.

But Lassiter betrays both the United States of America and the Confederacy as he wants to make California an independent "Republic of the Pacific" that he will despotically rule.

To this end, Lassiter commissions outlaw Luke Johnson and his gang to steal, by force, critical documents being transmitted through the town of St. Joe by Pony Express.

Roy risks limb and life to protect the mission of the Pony Express against the vicious outlaws, unaware of the Confederate agents supporting them.

Rogers, the Pony Express officials, and the cavalry then work out a plan which brings an end to the machinations of Lassiter and Johnson.