Deep within the Arctic Circle, three environmental scientists from the UK's Arctic Research Station trudge through a blizzard landscape in search of shelter. There's a cabin ahead. It appears abandoned. No lights or tell-tale smoke. No snowmobile parked outside. The first thing the team's medic, Dr Sheila Mackenzie, notices when she enters is the smell. It's rank, rotting, foetid. Then suddenly there's movement. A figure, barely recognisable as human, lies slumped on a sofa, his face staring back at her in the torchlight. It's hideously disfigured by livid pustules, rivulets of blood run from his nostrils, his chest covered in black bile. Momentarily Dr Mackenzie can't comprehend what she's seeing. Then the alarm bells begin to ring. These are the signs of chronic, deadly infection. But the man is trying to say something. She edges closer to him, and it's then that the convulsions begin.