The Canadians have discovered a valuable substance called Compound X, which can cure infantile paralysis. When a country at war with Canada learns that Compound X also contains magnetic properties that could aid them in their warfare against the British, they send agents to infiltrate Canada and steal a large quantity of the substance. It's up to Sgt. King (Allan Lane) and his Mounties to track down the agents and put an end to their scheme.

Escaped Prisoner 39013 impersonates the rich and influential Horace Granville, allowing him to create a variety of disasters. Fortunately, he is thwarted repeatedly by three daring circus daredevils.

The Three Mesquiteers are forced to track down a train robbery ring after some of the gang hijack their truck for a getaway and the police conclude they are part of the gang, an identification which is just fine with the gang's nameless chief.

American federal agent Clark Stuart is on assignment in Santa Fe to draw up a trade agreement with the newly installed Mexican governor. Meanwhile, Walter Jamison leads a wagon train from Missouri, hoping to take advantage of the new agreement. Among Jamison's passenger are famed frontiersman Jim Bowie and a very youthful Kit Carson. The destinies of all these personalities intersect when villainous ex-governor DuPrey schemes to undermine the treaty and take over the New Mexico territory for his own vile purposes. Somewhere along the way, Davy Crockett joins the "good guys" in their efforts to thwart the despicable DuPrey.

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. The Mesquiteers try again and send Lullaby to try and win some of the fake bills in a card game.

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.

The wealthy Van Dyke family are constantly in the media for outrageous behavior, much to the frustration of the patriarch, Dan Van Dyke. His self-centered wife has a fondness for foreign imports, including "pet projects" like dancers and such and his spoiled children Tony and Carol have constant run-ins with the law. When Dan himself ends up in the clink for five years for tax evasion, he becomes bunk-mates with ex-bootlegger Joe "Spots" Ricardi. Ricardi lectures him on being such a push-over for an out-of-control family, so a dying Dan makes Ricardi his estate trustee once he is released from prison. Ricardi is then thrust into high society and must do everything he once nagged Dan to do.