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...and the injured Colonel Emily Chaudhry knows UNIT has never backed down from a battle....

If UNIT is to fight back, it's going to need the services of its missing commander, Colonel Brimmicombe-Wood, and the experience of the Brigadier, who can never refuse when duty calls....

Written by Iain McLaughlin and Claire Bartlett and directed by Edward Salt.