One Step Forward, Two Steps Back was the thirteenth short story in the Short Trips anthology Short Trips: Defining Patterns. It was written by Chris Thomas. It featured the Second Doctor, Fifth Doctor, Jamie McCrimmon and Turlough.
The Doctor and Jamie visit Atkya at the time of the Yelyahj Peace Festival, which celebrates the end of renepscia syndrome, from which the Atkyans suffered until a cure was found a thousand years ago. Jamie has made a special friend of one of one of the Atkyans, Soji.
The next morning, the Doctor and Jamie are surprised to find Soji and the other Atkyans treating them like "scum". They are put into forced labour: the Doctor as a scientist, Jamie in the military. The Doctor deduces that somehow history has changed, and he and Jamie remember it differently from the other Atkyans.
- Unfortunately, the Doctor's cure has made the Atkyans aggressive and hostile. This is a side effect of the cure, which the Doctor hopes to fix.
The following morning, the Doctor and Jamie wake to an abandoned world. They access a program which explains what happened to the planet: the cure for renepscia syndrome caused the Atkyans to become aggressive and violent. The entire species has died out. To make matters worse, the person who engineered the cure was the Doctor — but a future version of the Doctor.
- The Doctor develops a stabilising agent to counteract the side effect of the cure. He tells Boksil and Lujet to make sure that the cure is always followed by the stabilising agent.
The Doctor and Jamie learn that the stabilising agent caused the metabolism of the Atkyans to speed up — each successive generation only lived half as long as the previous one. The Atkyans have died out. The Doctor explains to Jamie that he can't go back and change what his future self has done/will do. Once the timeline stabilises, his future self will suddenly remember this visit to Atkya.
- As the Doctor and Turlough leave Atkya, the Doctor is suddenly overwhelmed with the memories of his past self visiting Atkya in the future. He tells Turlough that they can't go back to Atkya because it would be dangerous to the Web of Time.
- The Doctor plays his recorder at the festival.
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