Ghost Light was the second story in Season 26 of Doctor Who. Although two stories followed its broadcast, it was the last story of the classic series to be produced and the last to feature significant recording at BBC Television Center.
The Seventh Doctor brings Ace to Gabriel Chase, an old house that she burnt down in her home town of Perivale near London. The year is 1883 and the house is presided over by the mysterious Josiah Samuel Smith.
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 housekeeper Lady Pritchard, the explorer Redvers Fenn-Cooper, who has seen something which has driven him insane, and the Reverend Ernest Matthews, an opponent of the theory of evolution which Smith has done much to spread.
The TARDIS arrives at Gabriel Chase. It turns out that Ace visited the house in 1983 and felt an evil presence. The 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.
In rescuing Ace, the Doctor releases an evolving creature trapped in the cellar, known as Control. The party moves to ground level. Control remains trapped in the cellar for the moment. The cellar is really a vast, stone spaceship. The Doctor works his way through the stuffed animals in Gabriel Chase and finds a human in suspended animation, 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.
The husks which attacked Ace were the remains of Smith, an alien who has been evolving into forms approximating a human and casting off his old husks as an insect would. For his pains, Smith transforms Matthews into an ape and places him in a display case. The Doctor helps Control 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 catalog all life on the planet. After completing its task and collecting samples (including Nimrod) 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 had lured and captured the explorer Fenn-Cooper within his den. Utilizing Fenn-Cooper’s association with Queen Victoria, he plans to get close to her so he can assassinate her and take control of the British Empire to make it a better place.
Light is displeased by all the change on the planet while he was asleep. While Light tries to make sense of it all, Smith tries to keep his plan intact, but events are beyond his control. Angry that his catalog is now missing the correct information, Light childishly decides to destroy all organic life to stop evolution after taking apart one of the maids to understand how humans work. He turns Gwendoline and her missing mother, revealed to be Mrs Pritchard, to stone in a bid to stop the speed of evolution. 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 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 down 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. In the end, with Smith the new Control creature imprisoned on the ship, Control, Fenn-Cooper and Nimrod set off in the alien ship to explore the universe.
The Doctor asks Ace if she has any regrets about burning the house now; Ace tells him she wishes she blew it up instead. The Doctor only smiles and says, “Wicked”.