Ben Taylor, an old prospector who has bragged extensively about his exploits apprehending criminals with the Mounties, loses the respect of his grandson when he turns over his hard-earned gold to a band of crooks. Sergeant Preston learns of the robbery and determines to capture the thieves with the assistance of Ben and his dog, Yukon King.
Sergeant Preston goes to Skagway, Alaska on a mail run and is asked to help solve a series of eight murders. With no official authority to arrest, he becomes Forty Mile Bill, a sourdough, and begins his investigation.
In the Beaufort Sea, the Snowbird, a ship rented by the Royal Geographic Society, is locked in the ice. Sir Philip and Coleville stay aboard while the Captain and crew abandon the ship. They are found by natives where Sergeant Preston finds them and the adventure begins.
Don and Jane Andrews are down on their luck and trying to sell their restaurant. He tried mining but the mine was worthless. Or was it? Sergeant Preston will find the truth.
Bart Larson, a police-hating killer jailed by Sgt. Preston, has broken out at Selkirk and plans revenge, before he returns to the U.S. with his partners. Unaware of the partners, Preston asks his superiors for permission to track Larson alone.
Fur trappers are being robbed on the trip home from the trading post. Preston and King must track down the trio dressed in black that have been committing these crimes.
Taggert and his cronies take over the remote trading post run by the Lloyds for financial reasons. They injure Dora's fiance Corey, saved from death by Metka Joe. Sgt. Preston and King take on the villians amidst the snow drifts.
In the Gold Creek area, Walt Seivers is shot. He had just struck it big. Sergeant Preston arrives and is wounded. Will Sergeant Preston solve this problem?
Bull and Pierre are two desperate murders who escape from Sgt. Preston's custody. They steal his dog sled team and the Mountie sends King after them know the husky will find them.
A dog named Mute leads Sergeant Preston to a hermit named Grizzly. Together they go after two fur thieves in an old mine where they are hiding after stealing furs at Elk River.