On Saturn, officers Buc and Huc are on patrol when they receive a signal stating that a denial is in progress. Meanwhile, the Doctor and Nyssa have seated themselves at a café to have some tea. Nyssa sees two young people trying in vain to find seats, and invites them to sit with her and the Doctor. They introduce themselves as Hel and Keet.
Meanwhile, four elderly Saturnites are hiding from authorities. Two of them, Lors and Raich, sneak out to steal food while the other two, Reen and Wend, wait. When Lors and Raich return with fruits and vegetables, Wend and Reen inform them that they've decided to accept their fate and take the next shuttle to Titan, as they feel it is unfair for them to stay. Reluctantly, Lors and Raich agree to leave Saturn as well.
Buc and Huc confront the Doctor, asking him his age. The Doctor jokingly gives his age, and is confused when they arrest him. They take him away, and Nyssa's new friends explain that as the Doctor is over one hundred years old, he is to be taken to Titan to work for the rest of his life. They invite Nyssa to their place to celebrate their having a baby.
The Doctor is taken to Titan by shuttle. Nyssa tries to find out where he is but is unable to board a shuttle to take her to Titan. She goes to the police station, where Buc and Huc give her the Doctor's ID so she can send him an e-letter.
On Titan, the Doctor meets Lors, and both of them are assigned to "litter and refuse". As they work, Lors tells the Doctor that he had wanted to stay on Saturn but was forced to come to Titan because he is over one hundred years old. He wants to find his wife Raich, who has also been sent to Titan. The Doctor suggests they escape.
Nyssa goes to Hel and Keet's party and asks if she can send an e-letter. As the Doctor is waiting for the right opportunity to cause a distraction, he gets a message from Nyssa. He lets her know where he is and asks her to wait for him on Saturn.
The Doctor and Lors find Raich, and the three try to board the next shuttle back to Saturn, but Raich doesn't make it in time. When they arrive at Saturn, Lors decides that he will go back to Titan because he'd rather be with Raich.
At the party, Hel and Keet announce the birth of their baby, and to Nyssa's shock, she learns that their son, who was born on Titan, will not come to Saturn until he turns twenty, and Hel and Keet will never meet him. Nyssa misses her family more than ever now. Hel tries to comfort Nyssa, and asks Nyssa to tell her about her family.
The Doctor and Nyssa finally meet up and leave the utopia of Saturn. Nyssa is saddened by the emptiness of the Saturnites' lives, but the Doctor says it is their choice.
Back on Saturn, Hel starts crying and asks Keet if their perfect life is worth never being able to meet their son.
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