Mycroft Holmes calls brother Sherlock in to investigate the theft of three key documents that expose the vital workings of the Bruce-Partington project -- a turn-of-the-century submarine which promises to make warfare against the British navy vitually impossible.

The apparent thief's body, that of a young government worker responsible for the documents' security, is found under strange circumstances along the tracks of the London underground. But Sherlock Holmes' search for clues begins to lead toward different conclusions than those of Inspector Lestrade.