Slightly more elaborate than most Charles Starrett westerns, Down Rio Grande Way is set in the mid-19th century, when the Republic of Texas was poised to join the Union. Starrett plays Texas Ranger Steve Martin, who is dispatched to a "renegade" Texas country that refuses to become part of the good old USA. He discovers that the crux of the problem is a local tax collector who, with the help of a crooked newspaper editor, is systematically robbing the citizens of their hard-earned cash, all the while fomenting anti-American sentiments.

In this western, three Texas Rangers decide to do their part to save the world and join the Army, but before they can, they are sent to Alaska to destroy a secret Nazi operation involving a submarine refueling station. The outpost is located behind an impenetrable tangle of barbed wire. The rangers get a little help, and discover a traitor. Then to get through the wire, they start a cattle stampede and save the day.

A woman doesn't realize that the man she has just married is a gangster. When she is implicated in a murder he committed, she turns to an ex-boyfriend, who is now a park ranger, for help. He hides her out in a cabin up in the mountains, and her husband goes on the hunt for both of them.