In this entry in the long-running series of westerns, the Three Mesquiteers transform their ranch into a prison farm to provide a model for prison reform. They are opposed by a local contractor who wants to build a standard prison.
Stony Brooke, Rusty Joslin and Rico, known as The Three Mesquiteers, return to Oklahoma at the close of the Spanish-American War, and are concerned that some of their wounded buddies have no prospects for a satisfactory future.
It's "The Three Mesquiteers" again. Gaucho escapes from Braden's gang only to be shot by them. The Mesquiteers drive away the outlaws and take his money on to his mother.
The Cherokee Strip is off limits to the Rangers, so that is where badman Lemar operates from. When the Rangers capture his brother and the jury sentences him to hang, Lemar starts killing the jurists.
A crooked real estate manipulator sells worthless land on mortgage to flood refugees, then tries to profit by reselling the land to the state, committing murder in the process, as the Three Mesquiteers work to bring him and his gang to justice.
After a payroll robbery the Mesquiteers catch up with the gang. But the members escape, the gang leader is killed, and they end up with only the leaders young son who is quickly sent to a work farm.
The Three Mesquiteers, as army scouts, soothe hostilities between the Army and Indians after both have been riled by someone with a hidden agenda - a renegade chief, who is found to be masquerading as an Army interpreter.
Stony Brooke, Rusty Joslin and Rico, the Three Mesquiteers, are returning from Mexico and are stopped at the border by Army officials, who are attempting to apprehend smugglers who are buying cheap silver in Mexico and smuggling it into the States, where they can take advantage of a silver stabilizing measure and sell it at a high price.
Harris and Rigby own a circus. Rigby is a counterfeiter and frames his partner. The Mesquiteers learn Rigby is the culprit and get a confession from one of his men only to lose the case when the man is murdered in jail.
This film was mainly shot in the Japanese skiing resort Hokkaido in 1937-38 and was intended to create support for the coming winter olympics of 1940 in Japan which however were cancelled because of the Japanese-Chinese war.
Herr Werther, a new magistrate to the Grand Duchy of Walheim who is a violinist and poet, seems to have fate on his side as he meets and pursues a beautiful local woman, Charlotte.