Fresh from confronting Moriarty in the end of The Great Game, Sherlock Holmes (Benedict Cumberbatch) and John Watson (Martin Freeman) are called to save the royal family from blackmail at the hands of Irene Adler (Lara Pulver), a dominatrix known as The Woman. Adler pulls Sherlock into a complex web of mysteries involving the CIA and the MOD, with secrets that could threaten to threaten international security and topple the monarchy.