Synopsis: Returning from Mezlob, a planet with an extremely heavy gravity, The Doctor and Jo must use the TARDIS' molecular adjuster to readjust their bodies for Earth's gravity. Jo gets in the chamber, just as the TARDIS is passing through a strange cosmic dust cloud. The Doctor notes that power levels have dropped throughout the TARDIS' controls, so he compensates by putting the molecular adjuster on "ultra-boost".
Jo is knocked out, but reawakens in a park in London. She sees two aliens in front of her, plotting to take over the world. Scanning around her, she sees the Doctor, and goes to warn him of the threat. The Doctor, however, cannot hear her. He continues heading to a small chapel, where he lays flowers on an open casket. As she gets nearer, Jo sees that she's laying in state!
Unable to attract the Doctor's attention verbally, she attempts to grab himóbut her hand passes right through his body. Jo believes she really is dead and is now a ghost.
Back at U.N.I.T. headquarters, the Brigadier alerts the Doctor to a flashing light in the laboratory. The Doctor explains that it is trying to warn them of a hole in the time-space continuum. He then sets about finding a way to shield the universe from this temporal contusion. As he works on the problem, though, he discovers that someone is trying to make their way through the hole. The person seems to be making direct telepathic contact with the Doctor.
Jo, meanwhile, has come to grips with her personal crisis and remembered the aliens she saw in the park. She purposes to try to find some way to warn the Doctor, so she makes her way back to the U.N.I.T. lab.
The telepathic voice inside the Doctor's head urges him to remove the "bandage" he's put around the rip in the fabric of space-time. When he does so, the Doctor can see Joóbut he can also see that he has died in U.N.I.T. headquarters!
The Doctor and Jo then move swiftly to the TARDIS and set a course through the "time-space gap". They narrowly make it through. Behind them, on a similar course, is a ship the Doctor identifies as a Breelian transporter ship. He worries about them getting a materializer through the gap, just as the gap closes and the ship is utterly destroyed.
Back now on the "right" side of the gap, this Doctor explains that the molecular adjuster had accidentally switched her with her counterpart in an alternate universe. This plane was the same one on which the Breelians existed, allowing Jo to see the Breelians when the Doctor couldn't. This also made Jo appear to die on the "right" side of the gap. Similarly, when the Doctor removed the "bandage" on the gap and chose to go through voluntarily, his "double" appeared to die in front of the Brig. Now that they had made it back through the gap together, the Doctor explains, their counterparts on the other side would simply "wake up" with no ill-effects.
Back at U.N.I.T. headquarters, our Doctor continues the explanation to our Jo and a very puzzled Brigadier. Jo, back to her normal self, quite sensibly brushes off the Doctor's ridiculously complex explanation and tries to shut him up by offering him a cup of tea.
Synopsis: Freedonia is a planet the Doctor, if not Jo, has visited before. When there last, he helped Kamoa fight in a revolution that the Doctor thought led to an era of peace and prosperity. But as he's shown around the city by the Freedonian, Bolgar, he's not so sure everything's as it should be.
From deep within the Freedonian laboratory, the Doctor's movements are being watched. Two Freedonians take note of the Doctor as he makes a device elsewhere in the laboratory.
Continuing to talk to Bolgar as he continues to use the laboratory's facilities. The Doctor's earlier suspicions are proved correct as Bolgar mentions that the reason there are no medical facilities on the planet is because disease has been eradicated. The Doctor turns to make an accusation, but is fired upon by Bolgar. The circuit jammer he's just constructed, though, fails to stop the particle beam, and the Doctor slumps to unconsciousness from the attack.
Jailed, the Doctor finishes his accusation to Jo. He's worked out that the "Freedonians" are actually robots. He just doesn't know why.
In the holding area with the Doctor and Jo are some of the real, flesh-and-blood Freedonians. They submit to their jailing because of a monster that lives in the underground cavern with them. As they're talking to the Doctor about their situation, the monster suddenly appears, taking the Doctor in its grip. Making a few adjustments to his circuit jammer, he uses it again. This time, the Doctor's efforts are more successful.
Back in the control area of the laboratory, the Freedonian robots that had been observing the Doctor are surprised he tried to use the device again. They're even more surprised that it worked. They send word to the jailor that they'd like to speak to the "illogical" Doctor.
When he arrives, Bolgar asks why he used the jammer again, after it hadn't worked before. The Doctor says he thought it might work, because Kamoa wouldn't "waste his precious brain cells" on the monster in the jail. Bolgar is surprised that the Doctor has guessed the planet's secret.
He reveals what the Doctor already suspects. The planet's population has largely been replaced by robots, except for those who were in the detention area. The elite, ruling class of robots have all been given Kamoa's brain cells, making them smarter and more resistant to simple interference, such as would have been generated by the Doctor's circuit jammer. The real, live Freedonians are kept detained, because they carry disease, weakness and vilolence with them. When the Doctor argues that Kamoa wouldn't have wanted his revolution to have resulted in this, the robot protests.
He takes the Doctor and Jo to an inner room, where Kamoa's actual brain survives. It speaks with the Doctor directly, contradicting what the Doctor has just said. In fact, this is exactly how he wanted the revolution to end up. What he noticed was that immediately after the revolution, the people descended into their old behavior. Fearing his cause lost, he decided to imprison most of the planet. Then he replaced them all with robotic copies, exact in most details, but devoid of pity or weakness. This allowed society to be more ordered and productive.
Jo points out that it has also replicated Kamoa's feelings of disillusion and bitterness throughout the new population. It has also turned the remaining flesh-and-blood Freedonians into fearful shadows of themselves.
Bolgar overhears this discussion and decides to pull the plug on Kamoa. The life support system attached to Kamoa's brain is suspended, and Kamoa's connection to individual Freedonian robots is ended.
The Doctor and Jo leave the planet to rebuild itself through a newfound spirit of cooperation between robotic and flesh-and-blood Freedonians.