A title card informs the viewer that Sir John Franklin's Arctic expedition was never seen again. In the opening sequence, James Ross is speaking to a Netsilik man in a tent who encountered the expedition's last survivors, under the leadership of Captain Francis Crozier, and informs Ross they were being pursued south by a creature called "Tuunbaq" and are now "dead and gone."
Four years earlier, in September 1846, Captain Sir John Franklin's Royal Navy expedition aboard HMS Erebus and HMS Terror are attempting the first crossing of the Northwest Passage in the Arctic Archipelago. The expedition runs into difficulty when a collision with an iceberg damages Erebus's propeller. Francis Crozier, captain of the Terror and second-in-command of the expedition, becomes concerned about becoming stranded in the pack ice above the Arctic Circle through winter, and recommends to Captain Franklin that they shift all men from Erebus to Terror and steam south aboard Terror to avoid becoming trapped in winter ice. Franklin overrules Crozier's concerns and presses the expedition further into the Passage in the belief that the ships can complete transit before the onset of thick ice. Before the ships can reach open water, however, they become frozen and trapped.
