David Collings

The Doctor, Sarah and Harry return to Nerva, but at an earlier point in time. The crew are dying from a space plague but the Doctor suspects a survivor may be responsible.

Sarah is the latest victim of the space plague and the only way to cure her is by transmatting her down to the surface of the mysterious planetoid, Voga.

The Cybermen who are intent on destroying Voga. The Doctor and two of the Nerva crew become walking bombs which they Cybermen will detonate once they reach their target.

Their plan to blow up Voga thwarted, the Cybermen intend to crash Nerva into the planet. Vorus is almost ready to launch his rocket at Nerva, but Sarah is still trapped on board.

At Brendon School, the Doctor enlists the help of the Brigadier. At Brendon School, Tegan enlists the help of the Brigadier. Same man, different time periods, however.

Mawdryn and his eternal mutants are awake and reveal the truth, they are exiles, they are in pain and need something only the Doctor can give them. His future lives.