In order to escape an attack in space, the TARDIS makes an unscheduled landing and ends up deep inside the London underground. Here the travellers soon find themselves engulfed in a terrifying battle against the Great Intelligence and the Yeti, a deadly enemy set to invade the Earth. As events progress and the menace spreads, it becomes clear that the intelligence's goal is not just possession of the Earth, but the Doctor's mind too...
 
This release includes all surviving episodes, plus a brand new fully animated black and white reconstruction of the missing episode created from the surviving audio- only recordings.