The Ark In Space
The TARDIS materialises on a fully automated space station, which appears to be empty and deserted. In reality it contains the whole future population of Earth stored away in deepfreeze until the planet – ravaged by solar flares – is again habitable. Due to a fault in the machinery they have failed to awaken on schedule. The Doctor discovers that the station has been invaded by the Wirrn, giant insect-like creatures, who have laid their eggs in one of the humans and plan to take over Earth. They have taken over the body of Noah, leader of the Ark.
Expelled from the Ark, Noah sacrifices himself and blows up the Wirrn. The Doctor, Sarah and Harry beam down to Earth to check the planet’s condition for the arrival of the humans from the space Station.