The Doctor takes Ace to Gabriel Chase. An old Victorian house which stands in the teenager's home town of Perivale. But the location and the name of the house is unknown to Ace as the Doctor has an ulterior motive for bringing her to the sinister building. As they make their presence in the house known to those who reside within It's walls. The Doctor and his companion discover an odd assortment of characters. Josiah Samuel Smith, an ambitious and ruthless man, who is not what he seems. Redvers Fenn Cooper, an eccentric explorer who saw something in the cellar of Gabriel Chase and has gone mad as a result. Josiah's Butler Nimrod who strongly resembles a Neanderthal. The stern housekeeper, Mrs. Pritchard and Josiah's pretty but unusual Niece Gwendoline. And then there is Control. A 'depraved monstrosity' as Josiah insists. A mysterious creature that is kept locked away in the Cellar of Gabriel Chase...