Here are summaries (warning—there are major spoilers) of episodes in season three.
Season Three (2014)
Episode 1: The Empty Hearse
Here’s a cleaner version that keeps the same level of detail as the Season Two rewrites while fixing the chronology and a few confusing bits:
“The Empty Hearse” (Episode 1)
Season Three begins two years after Sherlock’s apparent death. After a series of theories about how he survived his fall from the roof of St. Bartholomew’s Hospital, Sherlock is revealed to be alive and working abroad. Mycroft brings him back to London to investigate a possible terrorist attack.
Meanwhile, Watson has moved on with his life and plans to propose to his girlfriend, Mary Morstan. Before he can, Sherlock surprises him with the news that he is alive. The reunion does not go well. Watson is furious that Sherlock faked his death and allowed him to believe for two years that his best friend was dead.
Sherlock also reveals himself to Molly Hooper, Lestrade, and Mrs. Hudson, and word of his return quickly spreads.
Soon afterward, Watson is kidnapped and trapped inside a bonfire. Mary receives a cryptic text message leading her to Sherlock, and the two race to find Watson and rescue him before the fire reaches him.
At the same time, Sherlock investigates the disappearance of a passenger, Lord Moran, from a London Underground train. He eventually discovers a hidden Underground station and realizes that an unused train carriage beneath Parliament has been packed with explosives. Moran, a member of the House of Lords, is part of a plot to destroy Parliament during an important vote.
Sherlock and Watson find the bomb, but its timer has already been activated. Believing they are about to die, Watson finally admits how deeply Sherlock’s supposed death affected him and how much he missed his friend.
Sherlock then reveals that he has already figured out how to switch off the bomb. Watson realizes that Sherlock allowed him to believe they were going to die simply to force an emotional confession out of him, and he is understandably furious.
The bomb is defused, and Moran is arrested, but the episode ends with a glimpse of a mysterious figure watching footage of Sherlock rescuing Watson from the bonfire, suggesting that someone else has taken an interest in them.
Episode 2: The Sign of Three
DI Lestrade is closing in on a group of bank robbers when Sherlock sends him an urgent plea for help. Lestrade abandons the arrest and races to Baker Street with police backup—only to discover that Sherlock’s emergency is considerably less dramatic: he is struggling to write his best man’s speech for Watson’s wedding to Mary Morstan.
At the reception, Watson welcomes Major James Sholto, his former commanding officer in Afghanistan. Sherlock begins his best man’s speech, using stories from his adventures with Watson to explain their friendship. Among them is the unsolved case of the “Bloody Guardsman,” in which a soldier was somehow stabbed while standing guard in a locked shower.
As Sherlock talks, he connects that mystery with another seemingly unrelated case—and realizes a murderer is at the wedding. He concludes that Sholto is the intended victim.
Sholto retreats to his hotel room, afraid that he may put the other guests in danger. Sherlock, meanwhile, works out how the Bloody Guardsman was attacked: both victims wore tight military-style belts, and each was stabbed through the belt with a very thin blade. The belt temporarily held the wound closed, meaning the victim could continue walking without realizing he had been stabbed. Removing it could cause fatal bleeding.
Sherlock realizes that Sholto has already been attacked. He persuades him to open the door so that Watson, a doctor, can treat him before he removes his belt.
Sherlock then identifies the wedding photographer, Jonathan Small, as the killer. Small’s brother had served under Sholto and died during an operation in Afghanistan, and Small blames Sholto for his death. He has been using his job as a photographer to gain access to people connected to Sholto and determine how to kill him.
With Sholto saved and the killer caught, everyone returns to the celebration. Before leaving the wedding, Sherlock makes one final deduction: Mary is pregnant. He raises a toast to Watson, Mary—and their unborn child.
Episode 3: His Last Vow
Watson and Mary are asked by a neighbor to help find her drug-addicted son. Watson tracks him to a drug den, where he unexpectedly finds Sherlock, who claims he is there undercover as part of an investigation.
Sherlock is pursuing Charles Augustus Magnussen, a powerful newspaper owner who uses compromising information to blackmail influential people. One of his targets is Lady Elizabeth Smallwood, whom Magnussen is threatening with information about her husband’s past.
To get closer to Magnussen, Sherlock has begun a relationship with Janine, Mary’s bridesmaid and Magnussen’s personal assistant. Sherlock uses the relationship to gain access to Magnussen’s office, but when he arrives, he finds Mary already there—holding Magnussen at gunpoint.
Mary shoots Sherlock. Although badly wounded, he survives.
Sherlock later arranges a confrontation with Mary, and she reveals that before meeting Watson, she worked as an intelligence agent and assassin. Magnussen knows about her past and has been blackmailing her. Watson, whom Sherlock has secretly arranged to be present, overhears the confession and learns the truth about his wife.
Months later, Sherlock and Mycroft spend Christmas with the Watsons at the Holmes family home. Sherlock drugs the other guests and steals Mycroft’s laptop, then takes Watson to Magnussen’s estate. He offers Magnussen the laptop, which contains government secrets, in exchange for the information Magnussen holds on Mary.
But Magnussen reveals that Sherlock has misunderstood the source of his power. No physical archive contains his victims’ secrets: his “Appledore vaults” are a mind palace, and he has memorized the information he uses for blackmail. Sherlock therefore has nothing he can steal or destroy to protect Mary.
With no other way to stop Magnussen, Sherlock shoots and kills him in front of Watson and the authorities.
Rather than put Sherlock on trial, Mycroft sends him on a dangerous intelligence mission in Eastern Europe, one he is not expected to survive. Sherlock says goodbye to Watson and boards the plane.
Minutes after takeoff, television screens across Britain are interrupted by an image of Moriarty repeatedly asking, “Did you miss me?”
Sherlock’s plane is immediately ordered back to England.