The Doctor and Sarah answer a distress call and find themselves on Zeta Minor, the last planet of the known universe, where a Morestran expedition has gone missing.

The Doctor realises that Zeta Minor lies on the boundary between the universes of matter and anti-matter and something on the planet won't let the Morestrans leave.

The Doctor makes a deal with the Anti-Matter Beast to return all the anti-matter to the planet but Sorenson is determined to continue his research.

The Doctor tries to convince Sorenson to sacrifice himself for the rest of the crew but Salamar's attempt to deal with the situation causes their problems to multiply.

The Doctor and Sarah are drawn off course and, instead of UNIT HQ, they arrive on the same site in 1911.

The Doctor, Sarah and Laurence try to find a way to sever Sutekh's link to the mummies while poacher Ernie Clements finds the priory surrounded by a forcefield.

The Doctor and Sarah try to destroy Sutekh's rocket but the Osiran's mental powers prove too great for them.

The Doctor, Sarah Jane, and Scorby are trapped in the manor as a possessed Chase stalks them from within, while the gigantic Krynoid prepares to crush them from without. Worse, the alien plant is ready to germinate, spreading its seeds across England.