Old sourdough Si Moore is shot and his gold stolen from his isolated cabin. Moore makes his way to town for medical help and Sgt. Preston takes on the case. Preston is ambushed at a trading post by the robbers but a tribe of Indians helps him capture the fugitives.; Sgt. Preston goes undercover in Skagway, Alaska, to try to get information on who murdered Roger Morton to get $50,000 in gold.; After finding a rich gold strike, Bob Leyden returns to Dawson City to get backing from B. J. Summers, who has a daughter, Helen, who Leyden would like to marry. However, Frank Palmer, Summers' supervisor, is a romantic rival for Helen. Leyden's samples and map of his claim are stolen, but Sgt. Preston comes up with a plan to trap the thieves.