The Doctor enlisted the aid of Viking Eric the Red to retrieve the Plutonium. Once the Doctor and Eric succeeded, they went off to what would eventually become Nova Scotia. (PROSE: Who Discovered America?)
Behind the scenes
In the real world, Newfoundland was one of the earliest European colonial settlements in North America. Newfoundland would later become a colony of England and the United Kingdom, becoming a Dominion some time before the First World War. Newfoundland and Labrador eventually joined Canada, as a province, in 1949.