Series 26: Ghost Light

In 1883 the mansion house of Gabriel Chase in Perivale near London is under the control of the mysterious Josiah Samuel Smith, who has subjugated the occupants via some form of brainwashing. It is a most mysterious place, where the serving women brandish guns and the butler is a Neanderthal named Nimrod. Other occupants include Gwendoline, the daughter of the original owners of the house who have now disappeared; the calculating night housekeeper Mrs Pritchard; the crazed explorer Redvers Fenn-Cooper; and the Reverend Ernest Matthews, opponent of the theory of evolution which Smith has done much to spread. For his pains Matthews is transformed by Smith into an ape and placed in a display case.

The TARDIS arrives at Gabriel Chase. It turns out that Ace had visited the house in 1983 and had felt an evil presence, and the Seventh Doctor‘s curiosity drives him to seek the answers. Something is also alive and evolving in the cellar beneath the house and when Ace investigates she finds two animated and dangerous husks. The cellar is in fact a vast stone spaceship with something trapped inside. The Doctor, meanwhile, works his way through the stuffed animals in Gabriel Chase and eventually finds a human in suspended animation, an Inspector Mackenzie, who came to the house two years earlier in search of the owners. The Doctor revives him and together they seek to unlock the mysteries of Gabriel Chase. He also encounters the evolving creature from the cellar, known as Control, which has now taken on human form. The Doctor helps it release the trapped creature from the cellar, a being known as Light who takes the form of an angel.

Thousands of years in the past, an alien spaceship came to Earth to catalogue all life on the planet. After completing its task and collecting some samples, which included the Neanderthal, the leader Light went into slumber. By 1881 the ship had returned to Earth. While Control remained imprisoned on the ship to serve as the "control" subject of the scientific investigation, events transpired such that Smith, the "survey agent", mutinied against Light, keeping him in hibernation on the ship. Smith began evolving into the era's dominant life-form -- a Victorian gentleman -- and also took over the house. By 1883, Smith, having "evolved" into forms approximating a human and casting off his old husks as an insect would, managed to lure and capture the explorer Fenn-Cooper within his den. Utilizing Fenn-Cooper's association with Queen Victoria, he plans to get close to her so that he can assassinate her and subsequently take control of the British Empire.

Light is displeased by all the change that has occurred on the planet while he was asleep. While Light tries to make sense of all the change, Smith tries to keep his plan intact, but events are moving beyond his control. Light turns Gwendoline and her missing mother, revealed to be Mrs Pritchard, to stone in a bid to stop the speed of evolution; while Inspector Mackenzie meets a sticky end and is turned into a primordial soup to serve at dinner. As Control tries to "evolve" into a Lady, and Ace tries to come to grips with her feelings about the house, the Doctor himself tries to keep the upper hand in all the events that have been set in motion. The Doctor finally convinces Light of the futility of opposing evolution, which causes him to overload and dissipate into the surrounding house. It was this presence that Ace sensed and which caused her to burn the house in 1983. Also, Control's complete evolution into a Lady derails Smith's plan as Fenn-Cooper, having freed himself from Smith's brainwashing, chooses to side with her instead of him. In the end, with Smith now the new Control creature imprisoned on the ship, Control, Fenn-Cooper and Nimrod set off in the alien ship to explore the universe.

Cast
Doctor Sylvester McCoy (Seventh Doctor)
Companion Sophie Aldred (Ace)
Guest stars
Ian Hogg — Josiah Samuel Smith
Michael Cochrane — Redvers Fenn-Cooper
Carl Forgione — Nimrod
Sharon Duce — Control
John Nettleton — Rev Ernest Matthews
Katharine Schlesinger — Gwendoline
Frank Windsor — Inspector Mackenzie
Brenda Kempner — Mrs Grose
Sylvia Syms — Mrs Pritchard
John Hallam — Light

Production
Writer Marc Platt
Director Alan Wareing
Script editor Andrew Cartmel
Producer John Nathan-Turner
Executive producer(s) None
Production code 7Q
Series Season 26
Length 3 episodes, 25 minutes each
Originally broadcast October 4–October 18, 1989

source: wikipedia