Masterpiece Mystery Sherlock faces the biggest challenge of his life - delivering a best man's speech on John's wedding day. Sherlock ends up leaving the wedding early, and John may live to regret offering the role to a man who didn’t realize he was... (more) John’s best friend. Perhaps even more importantly, one of the guests at John’s wedding to Mary Morstan may not live to see the end of the day. it's too bad that that Sherlock is unable to focus his tremendous powers of deduction on the murder that’s hatching right under his nose, but then the responsibilities of a best man are more diabolically exhausting than preventing a very clever killing. Originally aired in the UK as Sherlock: Series 3, Episode 2