Chase is obviously under Krynoid control. The Doctor suspects possession but, with the mountainous Krynoid nearing maturity and whacking the mansion to pieces, he concerns himself with the bigger picture and orders the mansion - with Sarah and him still inside - to be bombed.

In the interest of self-preservation, Chase's men side with The Doctor against the Krynoid, but the Krynoid - now bigger than the Chase Mansion - invites The Doctor to join it, promising to leave the others alone if he does. People within a mile of the Chase Estate, however, start getting strangled by their plants, while Chase, snapping photos of the Krynoid, has a significant one-on-one encounter with it.

Sarah is saved from a Krynoid fate and runs off, but the same can't be said for one of Chase's men. Not only is he simultaneously devoured and transformed, his fascinated employer will do all he can to encourage the process. The Doctor gets introduced to Chase's grinder and compost acceleration chamber, which promises him a painful yet swift death en route to making him one with nature, via the garden's nutrient pump. The situation has finally gone too far for Dunbar, who outs his own involvement in this matter and stands up to Chase, only to come face to face with a fully developed Krynoid.

Surviving two attempts to end their lives, the Doctor and Sarah seek the identity of the plant fanatic who ordered the hit on the arctic base, pursuing their only lead - a commissioned painting of a rare flower left in the boot of a car. Chase, meanwhile, is doing all he can to encourage the hatching of the Krynoid pod.

With a killer Krynoid on the loose, the Doctor, Sarah and the last surviving member of the expedition concentrate on hunting it down, unmindful of Chase's men who, once they learn of the second Krynoid pod (which always travel through space in pairs), work to obtain it and eliminate all possible witnesses.

Members of the World Ecology Bureau discover a centuries-old seed pod buried deep in Antarctica's permafrost. It seems to be still alive, growing without soil. They transmit a photo to London where Richard Dunbar of the W.E.B. shares it with the Doctor. Wary of what it might be, the Doctor immediately flies down with Sarah. They don't know that Dunbar is a leak in the bureau and has tipped off the discovery to a rich plant fanatic named Harrison Chase. Chase sends a thug and a plant expert down to verify the discovery and fetch it back by any means possible. But before anyone arrives, the pod hatches and the tendril-like life form within attaches itself to one of the men, turning him green. It's as The Doctor feared: they're dealing with a Krynoid.

Morbius goes on the rampage, forcing the Doctor and Solon to team up to try and bring him back under control.

The Doctor attempts to restore the Sacred Flame to prove his good intentions to the Sisterhood, while Solon prepares to connect the brain of Morbius to his body.

The Sisterhood prepare to sacrifice the Doctor to the Sacred Flame and Sarah is injured while rescuing him.

The Tardis lands on the bleak planet Karn, in a spaceship graveyard, where The Doctor and Sarah find a evil scientist called Doctor Solon is constructing a new body for the brain of a evil time lord known as Morbius, whom The Doctor thought was executed by the high council on Gallifrey. Where Morbius with his new body plots to rule the galaxy.

The Doctor and Sarah reach Earth and try to warn the research centre about the Kraal invasion before Styggron unleashes his virus.

The Doctor is captured by Styggron and left to die in the destruction of the fake village but Sarah escapes from the disorientation chamber to try and rescue him.

The Doctor suspects Crayford brought something to Earth in his rocket, as he and Sarah find themselves hunted by UNIT.

The Doctor and Sarah return to Earth in the present day to find a strangely deserted village and woods stalked by white-clad figures.

Sutekh forces the Doctor to transport Scarman and a mummy to Mars, where the Doctor and Sarah try to stop them destroying the Eye of Horus.

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

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

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 problem to multiply.

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 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 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.

UNIT attempt to track down the Zygon ship while Broton prepares to have the Skarasen attack London.

The Doctor and the Brigadier begin to realise who the Zygon imposters among them are while Sarah discovers a secret tunnel to the underwater ship.

The Zygon traps the Doctor and Sarah in a decompression chamber while Harry is taken to the aliens' underwater ship.

The Doctor, Sarah and Harry are summoned back to Earth, where the Brigadier asks them to investigate the destruction of a series of North Sea oil rigs.