Doctor Who: The Ark — Paul Erickson

Materialising in what appears to be a jungle on Earth, the Doctor, Steven and Dodo soon realise that things are not what they seem: the sky is made of steel, and the jungle merely a colossal life chamber in a craft that has embarked on the most important expedition in the history of mankind...

It is ten million years in the future, and the Earth is soon to be engulfed by the Sun in a catastrophic explosion. A gigantic space ark has been launched, taking the last humans to a new life on the distant planet of Refusis, serving the Guardians of Earth are the Monoids, mute reptilian aliens.

But the Ark's mission of deliverance is threatened by the arrival of the time travellers; Dodo inadvertently passes her cold to the Guardians - to them, it is a long-forgotten virus against which they have no defence. It is not long before people start to die and the TARDIS crew are on trial for their own lives...