Enlightenment was the fifth story in season 20 of Doctor Who. It saw the introduction of the Eternals in their only televised appearance. It also saw the conclusion of the Black Guardian trilogy, with the redemption of Turlough and the first appearance of the White Guardian since The Ribos Operation.
A large number of model shots were used in this story to create the racing scenes and their associated locations.
Turlough’s sabotage of the TARDIS has left the control room dark and on back-up lights until the systems are repaired. Tegan and Turlough play chess. The Doctor thinks he hears a voice calling him. He instructs Turlough and Tegan to increase the power as he walks into the corridor. He sees the White Guardian having trouble materializing in the TARDIS. Trying to make out what the Guardian is saying, the Doctor learns danger awaits him. He is given a set of co-ordinates. Before the White Guardian can explain further, the Black Guardian appears and interrupts the communication.
The Doctor sets the co-ordinates and the TARDIS materializes in what appears to be a ship’s hold. Leaving Tegan in the TARDIS in case the White Guardian tries to contact them again, he and Turlough leave to explore, barely avoiding one of the officers with a mechanical, blank expression, dressed in an Edwardian naval uniform.
The Doctor speaks with the crew to learn they remember nothing of coming aboard. They have been below decks the whole time and the ship has been entered in some sort of race.
Tegan leaves the TARDIS and meets the ship’s first mate, Marriner. An officer with the same distant look escorts the Doctor and Turlough to see Captain Striker, who offers them dinner. The dinner is interrupted when the wind picks up and the officers announce that the race has begun.
In the wheelhouse, the Doctor sees a map of the race course, complete with “marker buoys” which he recognizes as the planets of Earth’s solar system. Marriner operates anachronistic electronic controls; a viewscreen activates to show the other contestants – a Greek trireme, a 17th century pirate ship and other vessels from other times, all floating in deep space.
Striker and his officers are Eternals, beings who live in the “trackless wastes of eternity,” as opposed to the Doctor and his companions, who are “Ephemerals.” As the ships round Venus, the trireme captained by Critas the Greek explodes when it tries to overtake the pirate ship. Striker believes it was the gravitational pull that did it, but the Doctor suspects otherwise. Tegan feels ill, so Marriner escorts her to a room which she soon realizes is a mixture of her room in the TARDIS and her rooms in Brisbane – they have been reading her mind. Marriner seems quite taken by Tegan, finding her mind fascinating and full of life.
In conversation with Striker, the Doctor learns that Eternals use Ephemerals for their thoughts and ideas. The Eternals have lived for so long they are unable to think for themselves. They need human minds to give them existence and entertainment — that is why the ships use human crews. The purpose of the race, however, is more than entertainment. The prize is Enlightenment, the wisdom to know everything.
The TARDIS is found by the Eternals, who make it vanish. Trapped on board the Edwardian ship, the Doctor and his companions go on deck in space suits. Turlough hears the voice of the Black Guardian taunting him, saying that he is doomed to eternal life aboard the ship. Unable to take the strain, he leaps overboard into space.
Turlough is rescued by the Buccaneer, the pirate ship commanded by Captain Wrack. She toys sadistically with Turlough with a knife, but he convinces her that he jumped overboard to throw in his lot with her, to find out the secret of how she will win the race. Wrack sends her first mate to present Captain Davey, one of the other competitors, with a jeweled sword, and party invitations to the other captains.
On board the Edwardian ship, Striker refuses the invitation, but the Doctor accepts, hoping to retrieve Turlough. Marriner offers to escort Tegan and the Doctor to the Buccaneer as an asteroid storm hits the ships. As Davey’s ship draws level with the Buccaneer, Wrack takes Turlough down in the hold and shows him the entrance to a locked chamber with a vacuum shield, but leaves him outside when she enters. Through the door, Turlough hears the voice of the Black Guardian. Davey’s ship explodes, apparently hit by an asteroid. The Doctor, though, again suspects otherwise, especially since, like Critas’s ship, Davey was also challenging the Buccaneer.
On board the Buccaneer for the party, the Doctor and Tegan mingle. Turlough sneaks off to examine the locked chamber. He finds an eye-shaped grid open to space, but a pirate locks the door and turns off the vacuum shield. Fortunately, the Doctor finds Turlough before he suffocates.
The Doctor notices the eye-shaped projector above the grid. He theorizes that this must be how Wrack transmits the power to destroy the other ships, with some sort of focus. He remembers Critas was wearing an out-of-period clasp with a red crystal. Turlough tells him of Wrack’s gift to Davey and the Doctor realizes the red crystal is the focus. Before they can act on it, they are captured by Wrack’s first mate. Meanwhile, Wrack has managed to lure Tegan away from the party to her wheelhouse. She freezes her in time and plants a red crystal in her tiara.
Brought before Wrack, Turlough accuses the Doctor of being a spy and claims he was trying to capture him. Wrack sends the Doctor, Tegan and Marriner back to the Edwardian ship. The Doctor believes Turlough is trying to prove himself trustworthy by stopping Wrack. Unfortunately, Wrack sees into Turlough’s mind. She is about to sentence him to walk to plank. She pauses when Turlough tells her that he, too, serves the Black Guardian.
As the ships near the crystalline space station of the Enlighteners, the Buccaneer pulls level with the Edwardian ship. Wrack brings Turlough again to the chamber, this time letting him witness her summoning the power of the Black Guardian. The Doctor, seeing the Buccaneer pull close, realizes the focus must have been smuggled aboard somehow. When he describes it, Tegan tells him about the crystal in the tiara. The Doctor smashes the crystal, but only multiplies the power by the number of fragments.
The Doctor gathers the pieces, rushes up to the deck and, just in time, hurls them overboard. They explode. The wind dies and Wrack pulls ahead of the Edwardian ship. The Doctor demands the TARDIS be released to him to stop Wrack from winning and Marriner reveals that it was concealed in the Doctor’s own mind. Travelling in it to the Buccaneer, the Doctor tries to reason with Wrack, but her first mate shows up with Turlough and she orders the Doctor thrown into space. While Tegan watches from the Edwardian ship, two bodies are ejected into space and the Buccaneer reaches the finish. The human crew of the Buccaneer vanish as Tegan, Striker and Marriner board to give their respects to the victor.
The Enlighteners turn out to be the Black and White Guardians and the winner is the Doctor, who brought the ship in with Turlough’s help when Wrack and her first mate met with an “accident.” The Doctor, however, refuses the diamond crystal holding Enlightenment, saying that he’s not ready for it. The White Guardian dismisses Striker and Marriner. Marriner resists; he wants to stay with Tegan. However, neither Tegan nor the White Guardian is moved by his pleading. Striker and he vanish into eternity.
As Turlough helped the Doctor bring the ship in, he is entitled to a portion of the prize. The Black Guardian reminds Turlough of their bargain and says that he can give up the diamond or sacrifice the Doctor to gain both Enlightenment and the TARDIS.
Turlough struggles with the decision. He hurls the diamond at the Black Guardian, who vanishes in screams and flames. The Doctor points out that Enlightenment was not the diamond, but the choice itself. The White Guardian warns again that the Black Guardian will return, even angrier now that he has been thwarted twice. He vanishes. Turlough asks the Doctor to take him back to his home planet, and the Doctor agrees.