2. The Sign of Three

It is John and Mary's wedding day and Sherlock is daunted by the task of delivering a Best Man's speech. As part of the speech, he recounts cases they have worked on including a soldier being stalked and somehow stabbed in a locked shower, a ghost dating women he dubs "The Mayfly Man", the last being part of John's disastrous stag night, among others. Before his speech ends, he realises that a murderer is present among the guests intent on killing John's old friend, Major Sholto. Sherlock saves the targeted guest, and then informs John and Mary of the meaning of the sign of three; namely that Mary is pregnant. The title and some of the plot is based on the Holmes novel The Sign of the Four.