Categorical Imperative ( short story ) Categorical Imperative was the seventh short story in the Short Trips anthology " " . It was written by Simon Guerrier . It featured the First Doctor , Second Doctor , Third Doctor , Fourth Doctor , Fifth Doctor , Sixth Doctor , Seventh Doctor , Eighth Doctor , Sarah Jane Smith , Ace , Charley Pollard , Jamie McCrimmon , Jo Grant , Susan , Peri and Tegan . Synopsis . " to be added " Plot . The Doctor has brought Sarah to a christening , but he seems in a bad mood . Sarah entertains herself by watching the queue of people waiting to give the baby his gifts . She notices that the baby ' s mother , who is named Ann , is surrounded by several young girls . Sarah wonders about their purpose , but when she nudges the Doctor , he says , " I know . Don ' t let him see you " . Surprised , she looks at the people in the queue , and is shocked to see the old Doctor that she knew before . She has a sudden suspicion about the baby . The Third Doctor carefully removes a silver knife from the package and prepares to use it . Jo is at the head of the queue with the mother , trying to distract her . An old man is at the front of the queue . He accidentally drops his present , and a silver knife falls out . He grumbles a bit and leaves , accompanied by his granddaughter , who had been up front with Ann . Sarah realises what the Third Doctor is about to do , and is appalled . The Fourth Doctor tells her that in fifty - two years , the baby will be murder ed by his aides for the devastation he caused . At the front of the queue , Ann is yelling at an American girl . The Third Doctor is at the front of the queue . He glances back , and sees behind him in the queue a large blond man . He notices that the man also has a silver knife , and is relieved that he doesn ' t have to be the one to kill the baby . He and Jo leave . While Peri takes her turn distracting Ann , Sarah wonders why the Third Doctor didn ' t go through with it . She sees an eccentric - looking blond man in the queue and asks her Doctor if that ' s him as well . As she looks down the queue , she sees several other eccentric looking men — a little guy in a straw hat , a young man in a beige coat and a man with a flashy silver cravat — and they are all carrying a silver knife . She wonders if they could all be Doctors . Underneath the chamber , the Doctor ' s TARDIS sits in a corner . The Fifth Doctor and Tegan enter and it dematerialises , but when the sound dies down , the TARDIS is still there . The Sixth Doctor and Peri arrive and enter , and the same thing happens again . Events repeat themselves when the Seventh Doctor and Ace arrive . Back in the chamber , Charley is talking to Ann . The Eighth Doctor is moving up the queue . The Fourth Doctor finally realises how to solve the dilemma . He sends Sarah off to Ann , and heads off . The Eighth Doctor approaches the baby , and Ann realises that he means to kill him . She yells for the guards , who subdue the Doctor . Ann looks at the face of her baby , and realises , for the first time , how much he means to her . Sarah is waiting below at the TARDIS . When the Fourth Doctor arrives , he explains that he helped the other Doctor get away . Sarah tells him that the other Doctor explained to her that things would be better , that the mother ' s affection would change the way the baby grew up . She also tells him that the other Doctor ' s TARDIS was parked on top of theirs , and that he and the girl Charley have already left . Sarah and the Doctor enter the TARDIS and it dematerialises , but this time , there are no police boxes left behind .