Those Left Behind was the sixteenth short story in the Short Trips anthology Short Trips: How the Doctor Changed My Life. It was written by Violet Addison. It featured the Fourth Doctor and K9 Mark II.
While there, they meet Debbie, Susan's best friend from Coal Hill School. Debbie, who turned fifteen that day, was concerned about Susan's sudden disappearance as she knew that Susan would never miss her birthday. She had met the First Doctor on one occasion but the Fourth Doctor did not recall seeing her before. He also did not remember Susan ever mentioning Debbie but admitted that he was not always the best listener.
He told Debbie that Susan decided to stay on 22nd century Earth but then amended this by adding that he chose for her, expressing the hope that this decision was for the best. Debbie was thankful that she met the Doctor as, while she knew that she would never see Susan again, she could at least live her life safe in the knowledge that she was safe in the future rather than spend it wondering what happened to Susan and fearing the worst.
- The Doctor offers to show Debbie the crystal temples of Canopus or the signing of the Magna Carta in June 1215.
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- Debbie notices Mr Chesteron's car parked outside of I.M. Foreman's junkyard at 76 Totter's Lane. (TV: An Unearthly Child)
- The Fourth Doctor arrives in London in November 1963 shortly after the departure of his first incarnation, Susan, Ian and Barbara (TV: An Unearthly Child) and shortly before the arrival of his seventh incarnation and Ace (TV: Remembrance of the Daleks).
- The Doctor tells Debbie that Susan decided to stay on 22nd century Earth but then amends this by adding that he chose for her. He hopes that this decision was for the best. (TV: The Dalek Invasion of Earth)
- The Doctor gives Debbie a framed black and white photograph of Ian and Barbara standing by a police box, waving at the camera and hugging each other. The frame contains a plaque that reads simply "1965". (TV: The Chase)