The Great Game is the Sherlock episode based in part on Arthur Conan Doyle’s story The Adventure of the Bruce-Partington Plans.
It is the third episode of the first series and uses a modern espionage mystery involving a missing government employee and a set of secret documents. The episode combines that Doyle source with several other story references, presenting Sherlock with a succession of apparently unrelated cases connected by coded challenges.
The Great Game is especially important because it introduces Professor James Moriarty as Sherlock’s principal adversary. Andrew Scott appears as Moriarty in the climactic pool scene, where the rivalry becomes explicit. The episode ends with Sherlock, John Watson and Moriarty facing one another while explosives threaten the situation.
The title is sometimes confused with The Final Problem, which is another series finale involving Moriarty, or The Reichenbach Fall, which develops the aftermath of their conflict. The Bruce-Partington source is therefore a useful way to distinguish The Great Game from the later episodes.