Dr Carr solved various cases thought impenetrable to Scotland Yard, which his friend, Henry Ransom, wrote up in best-selling novels. In 1920, he investigated the apparent murder of Sebastian Marten and Paul Steiffers at Lord Farthingale's country retreat.
At the climax of the case, he gathered the guests in the library, explaining that the murderer was the Broadway entertainer, Kitty Kickshaw, whom Sebastian Marten had identified as taking the identity of society hostess, Glenda Neil. Immediately after declaring this, the Ninth Doctor and Rose entered, explaining that the deaths were in fact a result of "invisible aliens". When Dr Carr protested against this, the Doctor challenged him to identify him from his appearance. Dr Carr failed.
A haze appeared, accompanied by a buzzing sound. Bart Faversham had started being lifted up and was tossed into the fire. The Doctor and Rose figured out that it was the drive of the invisible aliens' spaceship that was inadvertently causing this. The Doctor signalled the ship with standard galactic code of the 455th century to repair the ship.
When the haze subsided, Dr Carr investigated the police box Janet Farthingale discovered in her room. While he assumed that he would never see the Doctor and Rose again, they proved him wrong, and revealed that the blue box was their spaceship, in which they departed. (PROSE: Doctor vs Doctor)