A young Lieutenant in the British Army, serving in France in 1917. He and his men halted an ambulance which had been captured by the Germans, thus freeing Lady Jennifer Buckingham - the driver - and her passengers, whom she had picked up in the middle of No Man's Land. These were the Doctor and his companions, Jamie and Zoe. At the British HQ, Carstairs and Jennifer were called upon to take part as witnesses in a court martial in which the time-travellers were accused by General Smythe of being spies. Carstairs was unsettled by the proceedings, feeling the prisoners had not been given a fair hearing. He had been subjected to mental conditioning, and this was starting to break down. Speaking to Jennifer, he realised that both could not remember their recent past. He helped the Doctor and his friends escape and steal the ambulance from the HQ, and was with them when they drove through a strange bank of mist - to find themselves confronted by Roman soldiers.
Returning to the HQ they went to Smythe's private quarters and found evidence of alien technology hidden there. Carstairs' conditioning broke down fully and he accepted the Doctor's explanation that they were no longer in France but on some alien planet where a number of different battles from Earth's history were being fought in various time zones.
In the American Civil War zone, Carstairs was captured and taken to the alien command centre where he was reprocessed. He recognised Zoe as an enemy spy and was prepared to shoot her. The Doctor undid the reprocessing, and Carstairs then helped to lead the resistance movement which the Doctor initiated.
After the Doctor had summoned the Time Lords to come and stop the war games, Carstairs accompanied him and his companions back into the 1917 zone where the TARDIS lay. He then planned to go and find Jennifer, for whom he had formed a romantic attachment. The Time Lords returned him to his correct time and place in history.
His memory would have been wiped, but he had already proved himself adept at breaking mental conditioning.
Played by: David Savile. Appearances: The War Games (1969).
- First of three appearances in the programme for Savile. The second was as the scientist Winser in The Claws of Axos, and the most recent was as the Brigadier's replacement, commanding the UK contingent of UNIT, in The Five Doctors. He's married to Lois Baxter - Madam Lamia in The Androids of Tara.