Perivale, 1983

A column of smoke rises from the blazing ruins of a forgotten, decaying mansion.

Perivale, 1883

In the sleepy, rural parish of Greenford Parva, Gabriel Chase is by far the most imposing edifice. The villagers shun the grim house, but the owner, the reclusive and controversial naturalist Josiah Samuel Smith, receives occasional visitors.

The Reverend Ernest Matthews, for instance, dean of Mortarhouse College, has travelled from Oxford to refute Smith's blasphemous theories of evolution.

And in a deserted upstairs room, the Doctor and Ace venture from the TARDIS to explore the Victorian mansion...

Who – or what – is Josiah Smith? What terrible secrets does his house conceal? And why does Ace find everything so frightening familiar?