In 1845, Sir John Franklin sails HMS Erebus and HMS Terror into the Canadian Arctic with 128 men, searching for the Northwest Passage, and none of them come home. The film follows historians and forensic scientists picking through what evidence survives: skeletal remains on King William Island bearing cut marks consistent with knives, tinned food stores that may have leached lead into the crew's bodies, and nineteenth-century Inuit testimony describing starving white men, largely dismissed by the Royal Navy at the time as savage rumor. Forensic analysts explain what cut marks on human bone can and cannot prove, weighing the case for cannibalism against alternative explanations for the crew's collapse. The investigation moves between London's naval archives and the ice where the ships vanished, reconstructing a disaster that took the empire's best-equipped expedition and left nothing but scattered bones and a handful of cairns. The central question the film keeps returning to: whether the men held together to the end, or broke down and turned on each other once the food ran out.