The Doctor, Tegan and Turlough are enjoying a relaxing holiday on the Eye of Orion. The Doctor has used his time off to refurbish the TARDIS console.
On Gallifrey, a black-gloved figure operates a console. He looks through time, finds the first Doctor and uses a Time Scoop to lift him out of time. He places a figure of the Doctor onto a game board. On the Eye of Orion, the fifth Doctor feels a stab of pain.
At UNIT Headquarters, the second Doctor visits the Brigadier on his retirement.
They take a stroll on the grounds and are caught in a Time Scoop. Again, figures are placed on the game board and again the fifth Doctor feels a stab of pain from the loss and collapses.
The third Doctor is driving Bessie when he is caught by the Time Scoop. The fifth Doctor realizes parts of his past are being stolen. He must find his other selves.
Sarah Jane Smith leaves for work. K9 warns Sarah that there is danger and that the Doctor is involved.
The fourth Doctor and Romana are taking a ride on a boat at Cambridge when they are caught in a Time Scoop. However, they end up trapped in a vortex.
The fifth Doctor takes off in the TARDIS before fainting. Sarah Jane is caught by the Time Scoop.
The fifth Doctor begins to fade out as the TARDIS lands. They find themselves in a barren waste overlooking a grim tower. Figures of the Doctor, Tegan and Turlough are placed on the game board.
On Gallifrey, the High Council meets. They have over-ruled President Borusa and summoned the Master. They offer him a new regeneration cycle if he rescues the Doctor.
The first Doctor finds himself in a maze of mirrors. He meets Susan and the two soon encounter a Dalek.
Borusa shows the Master the game board — now identified as the Death Zone. It has been reactivated and is draining energy from Gallifrey. They wanted the Doctor's help, but he has been taken from time.
The first Doctor and Susan force the Dalek into a dead end, where the mirror bounces its beam backward, destroying it. They see the Dark Tower and realize they are on Gallifrey.
The second Doctor and the Brigadier are attacked by a Cyberman. Sarah meets the Third Doctor.
The first Doctor and Susan find the TARDIS. When the first Doctor takes the fifth Doctor's hand, the latter recovers.
The Council give the Master their seal and a transmat beacon. He goes into the Zone where he finds the remains of his predecessors.
The second Doctor explains that before Rassilon, his people misused their power. They would kidnap other beings and drop them into the Death Zone - a practice stopped by Rassilon. They must get to the Dark Tower, where Rassilon's Tomb lies.
The Master encounters the third Doctor, who refuses to believe he has come to help. A rain of energy bolts interrupts them and cripples Bessie.
The second Doctor wonders if Rassilon was as great a figure as rumored. Perhaps he is alive and running the game.
The fifth Doctor, Susan and Tegan set off for the Tower. The first Doctor tracks the progress of his other selves.
The second Doctor and the Brigadier climb into a tunnel below the Tower.
The Master meets the fifth Doctor and tries again to persuade him that he is there to help. They are attacked by Cybermen. The Master is knocked out and the Doctor takes the transmat beacon and operates it, escaping to Gallifrey. When the Master awakes, he offers his help to the Cybermen.
Susan and Tegan return to the TARDIS. The first Doctor and Tegan set off for the Tower again.
The Doctor accuses the Castellan of being in control of the Death Zone, based on a homing device within the transmat beacon. Borusa has his office searched.
The third Doctor and Sarah encounter a Raston Warrior Robot, a deadly killing machine. They are quickly cornered.
The guards find dark scrolls in the Castellan's rooms. They incinerate when Borusa inspects them. The Castellan proclaims his innocence but Borusa wants him subjected to the mind probe. Suddenly, there is a shot in the corridor — the Castellan has been killed trying to escape. Borusa refuses to let the Doctor return to the Death Zone.
The second Doctor and the Brigadier are attacked by a Yeti. The Doctor uses a flare to chase it off. They finally find their way into the Tower.
Cybermen find the TARDIS. After failing to break in, they set a bomb next to it.
Cybermen catch up with the Third Doctor and Sarah. The Raston robot attacks and destroys them, allowing the Doctor and Sarah to escape in the confusion.
The Doctor is not convinced that the Castellan was the traitor. Flavia agrees to investigate while the Doctor speaks to Borusa.
The third Doctor uses a metal line from the Raston robot to cross from a tall hill to the Tower.
The first Doctor and Tegan find their way into the front entrance of the Tower where a chessboard awaits. The Doctor finds that it is electrified if one steps on the wrong square.
The Master appears with the Cybermen. They force him to walk across the board first and he does so safely. When the Cybermen walk across, the board activates, destroying them. The Cyber Leader tries to force him to show the safe path, but the Master destroys him. The Master disappears into the Tower and the first Doctor figures out a safe way across.
The fifth Doctor enter the Council chamber but finds Borusa has vanished. The Doctor searches for a secret chamber.
The Doctors begin to feel the will of Rassilon pushing them back.
The third Doctor encounters Liz Shaw and Mike Yates. When they act strangely, he realizes they are illusions and pushes past them.
The second Doctor encounters Zoe and Jamie, who tell him to turn back. Realizing that they shouldn't remember him, he ignores the illusions.
The Doctors and their companions converge on a massive chamber with strange inscriptions and a body on an elaborate tomb. The Doctors translate the inscription — it promises eternal life to one who takes the Ring of Rassilon, but warns that "to lose is to win; and he who wins shall lose."
The Master arrives to help himself to immortality. But he is disarmed by the Brigadier.
The fifth Doctor finds the Harp of Rassilon. When he played the tune in a nearby painting, a secret chamber opens revealing the control room of the Death Zone. Inside is Borusa. He explains that he wants to become immortal and rule Gallifrey forever.
The Doctors deactivate the forcefield just before the Cybermen activate their bomb. The TARDIS moves to the Tomb.
Borusa uses the Coronet of Rassilon to dominate the Doctor's mind. He makes the Doctor bow to him and accompany him to the Death Zone.
Borusa freezes the companions. The Doctors refuse to cooperate and Borusa tries to dominate them. But they join their minds and resist him. Borusa is still defiant.
They are interrupted by the appearance of Rassilon's image. Borusa claims immortality. The Doctors dispute his claim, but the first Doctor supports the Lord President.
Borusa take the ring, but his immortality is to be frozen in stone on Rassilon's tomb, with others who have claimed immortality before him.
The Doctor asks that they be returned to their proper times. Rassilon agrees. He also frees the fourth Doctor and the Master.
The first Doctor explains that he suddenly realized what the cryptic inscription meant — immortality was a trap set by Rassilon for the power-hungry. The other Doctors and their companions depart in the TARDIS.
Flavia arrives and demands an explanation. She tells him he has been appointed President to deal with the crisis. He tells her to serve as his deputy before he returns in his TARDIS.
He jumps into his TARDIS and takes off. He explains to his companions that he has no intention of returning and will go on the run from his own people. After all, that's how it all started…