taxi is waiting for him. Outside, the cabbie confesses to the murders but proclaims he merely speaks to his victims, and they kill themselves. The cabbie challenges Holmes to solve his puzzle. Later, he pulls out two bottles containing an identical pill: one is harmless, the other is poison. Afterward, he invites the victims to choose one, promising he will swallow the other — and he threatens to shoot them if they refuse. Sherlock soon deduces the driver is an estranged father who was told three years earlier he was dying. The driver admits that he has a "sponsor" for his work, paying money for each murder for the driver's children. Holmes, having already noticed that the 'gun' is a novelty cigarette lighter, attempts to leave. However, the driver rechallenges him to choose a pill and see if he can solve the puzzle. Meanwhile, Watson has traced the GPS signal from the phone and followed the two men. He shoots the driver through a window in the adjacent building. Holmes tortures the cabbie to force him to say whether the pill taken was correct and who the sponsor is. He eventually reveals the name "Moriarty". The police arrive, and Holmes deduces the shooter is Watson but hides the truth from the police. Holmes and Watson leave the scene and run into the enigmatic man who claims to be Sherlock's arch-enemy earlier. He turns out to be Sherlock's elder brother, Mycroft, who works for the British government. Watson finally understands that Mycroft tried to bribe him out of genuine concern for Sherlock. Mycroft instructs his secretary to increase their surveillance status. Allusions The episode is loosely based on A Study in Scarlet and contains allusions to other works by Arthur Conan Doyle. Moffat said of "A Study in Pink" and A Study in Scarlet: "there are many elements of the story, and the broad shape of it, but we mess around with it a lot". Tom Sutcliffe of The Independent points out, "Fans will recognise at once that the close-reading Sherlock applies to John's mobile phone is drawn from an almost identical analysis of a pocket watch [taken from The Sign of the Four]. More slyly oblique is the conversion of the lost ring that Holmes uses to lure the killer in A Study in Scarlet into a lost 'ring', a mobile phone that can be used to contact the killer