The Doctor, Steven and Dodo have just arrived on Bukol on a passenger liner and are passing through customs. However, when the Doctor shows his visa, the image is of a different man. To the Doctor's shock, his companions denounce him as an imposter. The Doctor is taken away and interrogated by Yerma, who doesn't believe his story. He thinks the Doctor might be a criminal named Mykloz, who is a master of disguise.
Dodo and Steven, in the presence of a Bukolian guard, discuss the situation, wondering how the man could have tricked them into believing he was the Doctor. When Yerma brings the Doctor to them, Dodo attacks him, demanding to know where the Doctor is, and Steven threatens to kill him.
Yerma allows Dodo and Steven to accompany him on a search of the liner for their missing friend. They find an unconscious blond man who they say is the Doctor and who recognises them, with some surprise. They tell him that someone has been impersonating him. The Doctor is taken to a hospital to be treated for the injuries sustained in the attack on him. Meanwhile, Dodo and Steven enjoy a meal with Yerma. When he has to leave them briefly, they notice that a man is staring at them. Afraid, they run away, and he follows.
They manage to give him the slip and end up in an alley. They encounter the old man from customs, who they claimed is not the Doctor. He wants an explanation of what happened to them. Dodo apologises to him, but when Yerma arrives, she screams that the imposter is here. The old Doctor runs away.
As the Doctor makes his escape, he sees an old friend, Anu-Ak, who recognises him and brings him to his apartment. They see the Doctor on the news, listed as a fugitive, and Anu-Ak remembers that he has an old television transmission that can prove the Doctor's identity.
In a cell on the liner, the real Dodo sits in a corner while the real Steven paces the room, getting on Dodo's nerves. However, she eventually finds a hatchway, and with some difficulty they escape from their cell.
Meanwhile, at the hospital, an orderly injects the blond Doctor with something, and as the Doctor watches, the orderly's appearance shimmers and takes the form of Mykloz — from whom the Doctor is trying to rescue two Maleans. Mykloz gloats that he has injected the Doctor with a compound that will kill him and leaves the room. The Doctor tries to follow, but collapses on the floor.
Yerma watches Anu-Ak's television transmission.Despite its lack of a licence, Yerma is prepared to accept the Doctor's claim of his identity. A Bukolian official brings in the real Dodo and Steven, and they are glad to see the Doctor. However, Yerma is confused as to why they now claim that the old man is the Doctor. The Doctor concludes there are three imposters.
They head for the hospital to find the other "Doctor", but his hospital room is empty.
The Doctor and Yerma have much to discuss, so Dodo and Steven visit the carnival. A Bukolian official approaches them and tries to take them away, but is stopped by the blond Doctor. The official resumes Mykloz' appearance; he thinks Steven and Dodo are the other two Maleans and wants to kill them. The Doctor tries to convince him that they are the real Steven and Dodo, not the "mutant" Maleans that Mykloz is hunting. Mykloz runs off but is eventually captured by Bukolian officials.
When Yerma learns from the Doctor and his friends that Mykloz is a shape shifter, he is alarmed and they head for the detention centre. The deputy is dead and Mykloz is gone. Yerma tries to seal off the building, but "the deputy" has already left.
The blond Doctor watches two carnival performers. They are Orsa and Alëza, the "mutant" Maleans that Mykloz has been assigned to kill. The Doctor has brought them to Bukol for their safety. On Bukol is located the Sanctuary, a gateway to another dimension where the two Maleans can be safe. As they make their way to the Sanctuary, guided by the Gatekeeper, Mykloz tries to stop them. He fires a weapon, but Orsa and Alëza have passed through the gateway and are safe. The weapon's discharge reacts violently, and Mykloz disappears. The Gatekeeper tells the Doctor that Mykloz could be anywhere in space and time.
to be added
- The stories in Decalog are linked by the story Playback, in which psychic Silverman examines various items in the stranger's pockets. For this story, he examines the globe.
- This was the only story in the anthology to feature the Sixth Doctor, and it is a multi-Doctor story very much "hosted" by the First Doctor and his companions. This means that the Sixth is the only one of the then-seven Doctors not to get a "starring" role in any of the stories in the book.
- Anu-Ak shows the First Doctor a news report of a twin planet, whose inhabitants he had defeated at the Snowcap space tracking station in December 1986 before vanishing without a trace. (TV: The Tenth Planet)