The White Guardian appears in the TARDIS, warning the Fifth Doctor of great danger and giving him 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, the Doctor and Turlough leave to explore, barely avoiding one of the officers, dressed in an Edwardian naval uniform and having a mechanical, blank expression.
Speaking with the crew, the Doctor discovers they remember nothing of coming aboard, have been below decks the whole time, and that the ship they are on has been entered in some sort of race. Meanwhile, Tegan leaves the TARDIS and encounters the ship's first mate, Marriner, who offers to take her to her friends, whom he knows about even though he's not met them yet. An officer with the same distant look escorts the Doctor to see Captain Striker, who offers them dinner. However, the dinner is interrupted when the wind picks up and the officers announce that the race has begun. Going to 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 then operates anachronistic electronic controls and 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 and using solar winds for propulsion.
The Doctor speaks to Striker and discovers that he 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 that 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 finds out that Eternals use Ephemerals for their thoughts and ideas. The Eternals have lived for so long that they are unable to think for themselves and 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 discovered by the Eternals, who make it vanish. Trapped on board the Edwardian ship for the moment, the Doctor and his companions go on board deck in space suits. Turlough hears the voice of the Black Guardian taunting him and 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 with Turlough sadistically with a knife, but he manages to convince 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 jewelled sword, and to deliver party invitations to the other captains. On board the Edwardian ship, Striker refuses the invitation, but the Doctor accepts, wanting 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, however, Turlough hears the voice of the Black Guardian as 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.
Arriving on board the Buccaneer for the party, the Doctor and Tegan mingle while 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 then notices the eye-shaped projector above the grid, and theorizes that this must be how Wrack transmits the power to destroy the other ships, using some sort of focus. He remembers Critas was wearing an out-of-period clasp with a red crystal, and 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, however, they are captured by Wrack's first mate. Meanwhile, Wrack has managed to lure Tegan away from the party to her wheelhouse and freezes her in time while she 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 the Doctor. Wrack sends the Doctor, Tegan and Marriner back to the Edwardian ship. The Doctor believes that Turlough is trying to prove himself trustworthy by stopping Wrack. Unfortunately, Wrack sees into Turlough's mind and is about to sentence him to walk the plank. She pauses, however, 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, and Wrack brings Turlough once 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 that the focus must have been smuggled aboard somehow, and as he describes it, Tegan tells him about the crystal in the tiara. The Doctor smashes the crystal, but only manages to multiply the power by the number of fragments.
The Doctor gathers up the pieces, rushing up to the deck and just in time hurls them overboard as they explode. Suddenly, the wind dies, and Wrack pulls ahead of the Edwardian ship. The Doctor demands that the TARDIS be released to him to stop Wrack from winning, and Marriner reveals that it was concealed within 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 that the Doctor be thrown into space. As 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 containing Enlightenment, saying that he's not ready for it, and the White Guardian dismisses Striker and Marriner, who vanish back 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 a decision, and 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 once again that the Black Guardian will return, even angrier now that he has been thwarted twice, and vanishes himself. Turlough asks the Doctor to take him back to his home planet, and the Doctor agrees.
Doctor Peter Davison (Fifth Doctor)
Companions Janet Fielding (Tegan Jovanka)
Mark Strickson (Vislor Turlough)
Cyril Luckham — White Guardian
Valentine Dyall — Black Guardian
Keith Barron — Striker
Christopher Brown — Marriner
Lynda Baron — Wrack
Leee John — Mansell
James McClure — First Officer
Tony Caunter — Jackson
Clive Kneller — Collier
Writer Barbara Clegg
Director Fiona Cumming
Script editor Eric Saward
Producer John Nathan-Turner
Executive producer(s) None
Production code 6H
Series Season 20
Length 4 episodes, 25 minutes each
Originally broadcast March 1, 1983 – March 9, 1983