The Viking Symbol Mystery (Hardy Boys, Book 42);

The Canadian Northwest beckons Frank and Joe Hardy to mystery and adventure. It all starts when a French-Canadian trapper, Caribou Caron, makes a historical and valuable find–-a carved rune stone left by Vikings centuries ago near Great Slave Lake. When Caribou Caron attempts to sell the artifact to a representative of a museum, it is snatched by thieves. Like the intrepid Vikings of old, Frank and Joe, with their close pal Chet Morton, set off on a perilous quest in the Northwest Territories to recover the valuable artifact before the robbers can decipher the symbols leading to the buried treasure.