It was created by Steven Moffat and Mark Gatiss and stars Benedict Cumberbatch as Sherlock Holmes and Martin Freeman as Doctor John Watson.
Although the series depicts a variety of crimes and perpetrators, Holmes' conflict with his archenemy Jim Moriarty (Andrew Scott) is a recurring feature.
Meanwhile, Holmes is introduced to John Watson, a former soldier who served in Afghanistan, and the pair immediately move into a flat on Baker Street.
John Watson slowly gets to know and trust Sherlock despite police officer Sally Donovan (Vinette Robinson) warning him that Holmes is a psychopath and will one day be responsible for murder.
After a series of incidents, the person responsible for the deaths, a taxicab driver (Phil Davis), reveals that his victims took their own lives by playing a game of Russian roulette with two pills: one fatally poisonous, the other safe.
Some time later, Mycroft hires Sherlock and John to retrieve compromising photos of a minor royal, which are held on the camera phone of Irene Adler (Lara Pulver), a ruthless and brilliant dominatrix who also trades in classified information extracted from her rich and powerful clients.
When Adler discovers that the CIA are on her trail, she disappears and is then apparently killed, only to reappear to ask John to get her camera phone back from Sherlock.
Sherlock and John are contacted by Henry Knight (Russell Tovey), a man traumatised by the death of his father by a monstrous hound on Dartmoor years before.
Sherlock and John discover that the legendary hound is an ordinary dog used for publicity that the hallucinogenic gas makes appear as a demonic monster.
Moriarty launches a simultaneous heist on the Tower of London, Bank of England, and Pentonville Prison, crimes for which he allows himself to be captured and put on trial.
He secures not-guilty by intimidating the jury and visits Sherlock, explaining he still intends to "burn" him, taunting him with a "final problem" for him to solve.
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.
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.
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.
Sherlock, under the influence of drugs, enters his mind palace to solve a case from Victorian times about a bride shooting herself in the head and rising from the grave to kill her husband.
A figure from her past is bent on revenge in the belief that Mary betrayed him, but it is discovered that the traitor was the secretary of a British Parliamentary member.
Sherlock is contacted by the daughter of entrepreneur Culverton Smith, who she claims has confessed to a murder, but she does not know who the victim was as her father has used a drug on her that inhibits memory.
Sherlock deduces that her father is a serial killer and sets out to expose him, but he has returned to narcotics use since Mary's death and unable to clearly distinguish his own thoughts from reality.
Realising that she will continue to test him until someone he cares for dies, Sherlock tries to connect with her on an emotional level, offering the love and relationship with a brother that she never had, and Eurus stands down.