Quite simple the most hilarious and fun and probably the best episode so far in the series. It’s John & Mary’s wedding day; the first scenes sees DI Lestrade (Rupert Graves) and Sergeant Donovan (Vinette Robinson) are on the verge of arresting a criminal gang (or family) when Lestrade gets a few urgent texts from Sherlock asking for help. After calling for backup and racing to 221 B Baker street, he discovers that Sherlock is simply struggling to write a best man speech for John’s upcoming wedding to Mary. On the morning of the wedding both Mrs. Hudson, who is also attending, and Mycroft, who is not, tell Sherlock that marriage changes everyone. At the reception, John is delighted to see Major James Sholto, his former commander. Sholto lives in seclusion, having received death threats and media scrutiny after losing a unit of new soldiers in Afghanistan.
Sherlock, as best man, has his speech all prepared. Initially he starts off badly reading out the wedding telegrams, but he quickly discards them as being generic. He recounts the story of how John came to ask him to be best man and admits his deep love and respect for John. He also delivers a fabulous speech that I just had to watch a few times while laughing out loud! Sherlock then launches into a rambling narrative, describing the importance of John in an attempted murder he and Watson had worked on, “the Bloody Guardsman”; a case they never solved of a guardsman, who had contacted Sherlock & Watson saying he was sure that he was being stalked by a man with a camera, who killed while in the shower alone and with no weapon or escape route in sight! Sherlock cites it as an example of John’s compassion; instead of trying to solve the murder as Sherlock did, John examined Bainbridge’s body and discovered that he still had a pulse, thus requesting an ambulance and saving his life. Later, after Sherlock recounts his & John’s attempt to drink a pint each at a bar on the same streets as the cases they have worked on, they get another case. several days after going to a man’s apartment for dinner, a woman who worked as a private nurse found that the apartment was vacated, and that the man was listed as having died weeks ago. Sherlock and John, still inebriated from John’s stag night, attempted to search for clues, but were arrested instead. The next morning, an amused Lestrade secured their release from jail. Sherlock chatted to other London women with a similar experience, but failed to find any significant connection between them. With John’s help, he concluded that the perpetrator was a man bored with marriage, who disguised himself as recently deceased single men and used their unoccupied homes to meet the women.
As Sherlock is winding his speech and about to toast the newly wed couple he freezes recalling that the nurse knew John’s middle name (Hamish). Since John never uses it, Sherlock deduces that the nurse had seen it in a wedding invitation. Sherlock concludes that all of the women who worked for Sholto in various capacities and were bound by confidentiality, were women that this mysterious man dated once! The Mayfly Man courted them to find and attack Sholto, and the wedding is his chance. Sherlock informs Sholto who then goes to his room and gets his gun. Sherlock, John, and Mary race to the room to try and save him, but he refuses to open the door until the case is solved. Sherlock deduces that the Bloody Guardsman case is linked to Sholto’s, and pinpoints the military uniform both wore as the common link; since Bainbridge collapsed in the shower, he must have been stabbed with a stiletto-type blade beforehand, but with his military waist belt firmly holding the flesh together, the damage would not take effect until the belt loosened. Upon hearing this explanation, Sholto contemplates suicide by loosening his belt and bleeding to death, as he has been severely depressed from the loss of his unit and the subsequent public animosity. Sherlock convinces him not to, primarily by insisting that it would be cruel to do at John’s wedding. Sholto then opens the door and requests medical assistance.
Later that evening Sherlock has the photographer brought back to the hall and identifies him to Lestrade as Jonathan Small, the Mayfly Man, deducing that he was the only person who could have stabbed Sholto. He points out that the photographer’s brother was one of the men killed under Sholto’s command, and concludes that he stabbed Bainbridge as practice for this murder. After Sherlock plays the violin for John and Mary’s first dance, he quietly reveals to them that he has observed in Mary “increased appetite, change in taste perception, and sickness in the morning, the signs of three”, implying that she is pregnant. Last shot shows Sherlock leaving the hall alone, while everyone else dances and enjoys the evening.