 A foreign power, which is represented by their agent Marlof, attempts to set up secret missile bases in Canada to target the United States for their planned summer invasion.Meanwhile, acting on intelligence following the smashing of a spy ring in Montreal, Royal Canadian Mounted Police (RCMP) officers Don Roberts and Kay Conway go undercover in a settling party headed for the Yukon.Marlof also has agents, Beck and Reed, in the party en route to the site of the planned missile bases.