Two years on from reports of his Reichenbach Fall demise, Sherlock resurfaces as London comes under threat of a huge terrorist attack. John, though, has mixed feelings – he's delighted by the return of his best friend, but harbours worries that the consulting detective's reappearance will have an adverse affect on his settled domestic life, in particular his romance with Mary Morstan.

Sherlock faces his biggest challenge of all – delivering a Best Man’s speech on John’s wedding day! But all isn’t quite as it seems. Mortal danger stalks the reception – and someone might not make it to the happy couple’s first dance. Sherlock must thank the bridesmaids, solve the case and stop a killer.