A reluctant Solomon (Colin Baker), along with his former associates Egan (David Troughton) and Saul (John Wadmore), have (they think!) escaped Earth and returned to their own dimension. But a mysterious force returns them to Earth and drops them right into the middle of a top-secret experiment involving a young girl's mind powers. They soon find that the experiment has gone wrong and unleashed something deadly...and unless they can find a way to stop it, they and the experiment's team members will all soon be dead!

Two years have passed since the Nestene creature vanished from UNIT's top secret Warehouse... Suddenly and without warning the Nestene strikes, once again using Autons as its deadly foot soldiers. As mysterious UNIT operative Lockwood struggles to unearth the Nestene plan, he finds himself drawn to remote Sentinel Island. There, the population have been caught up in a bizarre frenzy of religious activity. Lockwood is joined by Natasha Alexander, a new scientific advisor with her own, sinister agenda. To defeat the Nestene menace they must both face the terrifying power of a creature from before the dawn of Mankind...

The space solar yacht Tiger Moth under the command of no-nonsense Captain Lisa Deranne is on a cruise taking some rich misfits on a voyage through space. Unfortunately on their travels they have picked a stowaway, a shape-changing Rutan, a race that has been at war with another race, the Sontarans, since the dawn of time. The Rutan has important news regarding the war and the Sontarans, and upon hearing the news, attack the Tiger Moth and take it over. The Rutan hides itself among the crew and one by one the Sontarans and the human crew are murdered by the Rutan. The Sontarans plan to destroy all life on the Tiger Moth. Can Lisa find out who the Rutan is before the Sontarans destroy her ship and her life?...