Season 3

Complete listed story — includes the ending

1. The Empty Hearse

Two years after his reported Reichenbach Fall demise, Sherlock, who has been cleared of all fraud charges against him, returns with Mycroft's help to a London under threat of terrorist attack. He tries to convince John—who has moved on and now has a girlfriend, Mary Morstan ( Amanda Abbington )—to help; however, John is angry that Sherlock did not tell him he was alive. Instead, Sherlock enlists Molly to assist him, but when John is kidnapped by unknown assailants and is rescued by Sherlock and Mary, he returns to help find the terrorists and foil an underground plot to blow up the Houses of Parliament during an all-night sitting on Guy Fawkes Night. Based on the short story " The Adventure of the Empty House ", and " The Lost Special " with numerous references to other works by Sir Arthur Conan Doyle, and other adaptations of the original stories.

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.

3. His Last Vow

Stolen letters lead Sherlock into conflict with Charles Augustus Magnussen, "the Napoleon of blackmail" who knows the personal weakness of every person of importance in the Western world. During the investigation Sherlock is shot and nearly killed by Mary, who is being blackmailed by Magnussen. After waking up from near-death, Sherlock escapes the hospital and lures Mary to an abandoned building, where he tricks her into revealing her false identity and attempted murder while John is listening nearby. Months later, Sherlock drugs everyone at the Holmes family Christmas party and steals Mycroft's laptop full of state secrets, and he and John take the laptop to Magnussen to trade for all of the files on 'Mary Morstan'. It is revealed that Magnussen keeps no files; it is all in his near-perfect " mind palace ". To protect John, Mary, and their forthcoming child, Holmes kills Magnussen in front of Mycroft and several other witnesses, and as a result is sent off on a suicidal assignment overseas. However, he is brought back almost immediately because of a video being broadcast all over England with Jim Moriarty's face asking "Did you miss me?" The title is based on Doyle's short story " His Last Bow ", whereas the plot contains elements of two other short stories, " The Adventure of Charles Augustus Milverton " and " The Man with the Twisted Lip ".