Plot summary
The police investigate a series of deaths related to people who all appear to have committed suicide by taking a poisonous pill. They turn to their unofficial consultant, Sherlock Holmes, who deduces various elements pointing to a serial killer. Meanwhile, Holmes is introduced to John Watson, a former soldier who served in Afghanistan, and the pair immediately move into a flat on Baker Street. John Watson slowly gets to know and trust Sherlock despite police officer Sally Donovan ( Vinette Robinson ) warning him that Holmes is a psychopath and will one day be responsible for murder.
Sherlock's brother Mycroft ( Mark Gatiss ), at first not revealing his identity, arranges a meeting with Watson and asks whether he will spy on Sherlock for money, but John refuses. After a series of incidents, the person responsible for the deaths, a taxicab driver ( Phil Davis ), reveals that his victims took their own lives by playing a game of Russian roulette with two pills: one fatally poisonous, the other safe. Before Sherlock can play the cabbie's game, John shoots the cabbie from an opposite building. Before he dies, the taxicab driver reveals that " Moriarty " was his sponsor. Loosely based on the first Sherlock Holmes novel, A Study in Scarlet.
Credits
Adapted from Wikipedia contributors, List of Sherlock episodes. HTML formatting and reference markers removed.