Responding to an advert apparently worded for him alone, Captain Mike Yates (retired) is reunited with a ghost from the past. But why has the Doctor, that mysterious traveller in Time and Space, sent for his former UNIT acquaintance? Trapped by a horde of vicious creatures in an apparently innocuous English country cottage, the two old friends are on the brink of an enormous adventure. As the Doctor relates his recent escapades, it becomes clear to Mike that they - and the Earth at large - are facing an enemy of unimaginable power and horrific intent.