The universe stands on the brink of a dimensional crisis - and the Doctor and Raine are pulled into the very epicentre of it. Meanwhile, on Earth, UNIT scientific advisor Dr Elizabeth Klein and an incarnation of the Doctor she's never encountered before are tested to the limit by a series of bizarre, alien invasions. At the heart of it all is a terrible secret, almost as old as the Time Lords themselves.

Gallifrey is in a state of crisis, facing destruction at the hands of an overwhelming enemy. And the Doctor is involved in three different incarnations - each caught up in a deadly adventure, scattered across time and space. The web of time is threatened - and someone wants the Doctor dead. The three incarnations of the Doctor must join together to set time back on the right track - but in doing so, will they unleash a still greater threat?

The Doctor and Peri find themselves in the Museum of Aural Antiquities, where every sound is stored for posterity - from the speeches of Visteen Krane to security service wiretaps and interrogation tapes. But they also find an intruder, mysteriously changed recordings, and a dead body. Before long the Doctor realises that there is more going on than a simple break-in or murder. How can he defeat a creature that is made of pure sound? Written by Justin Richards. Directed by Gary Russell.

Ares One: NASA's first manned mission to the dead planet Mars. But is Mars as dead as it seems? While the NASA team investigate an 'anomaly' on the planet's surface, the Doctor and Peri find themselves inside a strange alien building. What is its purpose? And what is frozen inside the blocks of ice that guard the doorways? If the Doctor has a sense of deja vu, it's because he's about to meet some old adversaries as well as some new ones.... Written by: Justin Richards. Directed by: Gary Russell.

Landing in Alaska, the Doctor and Nyssa encounter a group of people in a most unusual house, cut off not only by the harsh climate but by their individual secrets and obsessions. Millionaire Shaun Brett is utilising chunks of the local area to construct a shrine to his dead father. But when deadly creatures start roaming outside and a terrifying discovery is made inside the house, the Doctor realises that Brett has unleashed an unimaginably ancient force. Written by Stephen Cole. Directed by Gary Russell.