McKenna of the Mounted

In this north-western set in the Yukon, a Mountie must investigate the violent deaths of three mail carriers.

Constable Ward is assigned to track down a mysterious villain known only as The Leader. Trying to locate a secret gold mine, The Leader pits the Indians against the Mounties, whom he blames for creating trouble.

Assigned to catch a gang of outlaws, officers Bruce Kenton and Paddy Halloran rescue Helen Morgan when her wagon is attacked by the very same gang. Through a ruse, Kenton manages to infiltrate the gang, which is holed up in the lawless community of Caribou Flats. While in the employ of villainous trading post operator Jack Blake, Kenton discovers that Blake is not only the leader of the gang but also the man who murdered Helen's brother.

In the great white north, a trapper searchers for the thief who has been stealing his furs while a local trader seeks to take advantage of the situation.

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.