"All organic life will be destroyed in the firestorm and when this world is destroyed there will be no more change, no more evolution and no more life..."

Earth 1883. At the heart of a Victorian house by the name of Gabriel Chase, lies an alien ship. For millions of years its owner has been asleep, unaware that part of the cargo has evolved into a malevolent creature. When the Doctor brings his assistant Ace to the house to face and overcome a terrible fear from her past, he finds himself catapulted into the secrets lying dormant there. Who or what is the alien presence Josiah? What has he done with the real inhabitants of the house? More importantly, of what is Josiah so frightened and can it help the Doctor? In order to combat Josiah's evil presence, the Doctor arranges the release of a more powerful entity called Light - the true owner of the alien ship. However, as events unfold the Doctor discovers he may have awoken an even more dangerous adversary.

For Light means to destroy every living thing on Earth...

Originally transmitted 04/10/89 - 18/10/89