A deadly flu-like infection is sweeping the planet. Its first cases appeared in Britain but now millions are infected worldwide and there is no sign of a cure. The emergency services can't cope with what the press have dubbed a plague. Under attack from all sides, UNIT in Britain is in disarray. It faces a stark choice - to close its doors and concede defeat, or to fight back, whatever the cost. The injured Colonel Emily Chaudhry knows UNIT has never backed down from a battle.