Kate Forbes is attending the funeral of her father, businessman Bernard Forbes, who was killed in a car accident. After the ceremony, she sees a strange-looking man talking to her mother. Her mother says that, according to the man, Bernard is going to live again.
Tuala has broken into UNIT headquarters. She makes her way to the Doctor's laboratory, surprising the Doctor and Jo, who she thought wouldn't be there at this time of night. She grabs some equipment and takes Jo hostage. Unknown to Tuala, the Brigadier has attached a homing device to her getaway car, and the Doctor follows the girls in Bessie.
Tuala blindfolds Jo and brings her into a house. When they get inside, they both experience a painful sensation. After it passes, they head upstairs, to find the landing barricaded with furniture. They remove the furniture and enter a bedroom.
The Doctor has reached the house, which is in great condition compared to the surrounding dilapidated houses. In the house he finds a safe, guarded by a force field. He retrieves a newspaper from the safe, and reads a headline about Bernard Forbes' death. He goes upstairs after hearing a scream.
Upstairs, he tries to get Tuala to talk, realising that she is not from this time. However, she uses a black box to transport herself and Jo away. As the Doctor is holding the newspaper it disappears too.
Jo and Tuala are in the same room at a different time. Jo recognises that Tuala comes from the future when the Daleks had invaded Earth. Suddenly they hear their own voices outside the door and experience the same painful sensation as before. Tuala explains that the energy release is from two versions of themselves in close proximity. Tuala has decided to convince her uncle, Krashen, to ask the Doctor for help fixing their time machines.
The Doctor and the Brigadier visit Annie Forbes to talk about her husband's death. They are surprised to see he is alive, though he seems to have lost some of his mental abilities. The Doctor explains to the Brigadier that Krashen is changing history, probably for money. The problem is that not only is he creating paradoxes, he himself is a paradox because he comes from a timeline that the Doctor had already changed.
Tuala and Jo meet Krashen at a church. He's angry at Tuala. She tries to convince him that their time machines are killing them.
The Doctor meets Krashen at the house. He tries to convince him that he has to stop, that the timeline including the Dalek invasion has been changed. Krashen tries to justify his changing of history. The Doctor points out that time is destroying the house, Bernard Forbes, and Krashen himself. Krashen uses his machine to take himself and the Doctor to the bedroom at the time Jo and Tuala were in it. Tuala and Krashen fade away. The Doctor and Jo then barricade the landing to delay the entrance of the earlier Jo and Tuala. The Doctor fixes the time machine and the room explodes.
The Doctor and Jo wake up in UNIT sickbay. The Doctor is dismayed to find no mention of Bernard Forbes' death. He goes to the Forbes house, where Annie Forbes tells him that Bernard just vanished.
- Third Doctor
- Jo Grant
- Brigadier Lethbridge-Stewart
- Bernard Forbes
- Kate Forbes
- Annie Forbes
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