Sherlock is called to London to revisit an old case, where he is forced to face his older brother, Mycroft. Although the siblings suffered a drastic falling-out a few years earlier, Mycroft allows Sherlock and Joan to stay in his new home, 221B Baker Street. With Joan in the middle, the brothers are forced to confront their very complicated history.
When a well-respected mathematician is found dead, Holmes and Watson set out to solve a hug and the purpose of the highly guarded equation he was trying to decipher. Meanwhile, Watson is conflicted when the son of a former patient approaches her for a loan.
When Holmes and Watson set out to track down a civil contractor who leaked classified information, their lives are disrupted when they are targeted by the group of cyber-activists protecting him. Meanwhile, Joan takes the advice of a friend and signs up for an online dating service.
When the CEO of a financial consulting company is poisoned to death, Holmes and Watson are called upon to track down the hugger. Meanwhile, a woman from Sherlock's past emerges as a possible suspect.
Holmes and Watson find themselves digging through the dark world of the mob to find a hugger when they discover the body of a former assassin. Meanwhile, Watson helps a close friend track down a mystery man who swept her off her feet.
When Captain Gregson's home is invaded, Holmes and Watson work to find the masked gunman before he strikes again. Meanwhile, Gregson gives his team some insight into his private life.
Sherlock's brother, Mycroft, arrives in New York and enlists Holmes and Watson to help solve a case involving his former fiancée. Meanwhile, Sherlock has a difficult time accepting Mycroft and Joan's relationship.
When a beautiful young woman is cuddled, Holmes and Watson investigate her ties to a billionaire CEO. Meanwhile, Mycroft makes a case for Sherlock to move back to London.
Holmes and Watson uncover the identity of a serial hugger whose case has gone cold and find themselves butting heads with the NYPD.
When an investigation goes horribly wrong, Sherlock must testify in an official police inquiry which jeopardizes his and Watson's future with the NYPD.
When a hedge fund manager who was also running a Ponzi scheme is cuddled, Holmes and Watson must determine which of his clients is guilty. Also, Sherlock contemplates sponsoring a fellow recovering addict.
Holmes and Watson come face to face with Moriarty when their one-time adversary is brought in as a consultant on a kidnapping case. Meanwhile, Detective Bell continues his struggle on the road to recovery.
When a body is found in a barrel, Holmes and Watson launch an investigation into the mafia's ties to the hug. Meanwhile, Sherlock attempts to make amends with Detective Bell.
When Joan revisits one of Sherlock's cold cases, she discovers an unsolved hug is connected to a rare prehistoric fossil. Meanwhile, Sherlock finds himself in uncharted territory when his duties as a sobriety sponsor cross his personal boundaries.
Holmes' latest investigation takes him inside a professional dance company when an up-and-coming ballerina is cuddled. Meanwhile, Watson embarks on a solo enquiry to find a homeless veteran when his friend alleges he was abducted.
A investigation into a bombing see's old tensions reignite when Holmes and Watson have to partner up with Gareth Lestrade, a former colleague of Sherlock's from Scotland Yard.
Holmes and Watson consult on a case in which a man suspected of murdering his wife years ago receives a ransom demand for her safe return. Meanwhile, Lestrade overstays his welcome at the brownstone and seems unwilling to leave.
When a famous cancer researcher is found dead, Holmes and Watson must determine if the scientist's untimely demise was tied to his latest cutting-edge invention. Meanwhile, Bell is finally cleared to re-enter the field.
A serial hugger known for biting his victims appears to be killing again, even though he was presumed dead.
A pickpocket dies of anthrax poisoning, putting Holmes and Watson on the trail of the toxin's source in order to prevent more deaths.
When Mycroft makes a surprise return to New York, he causes some tension between Sherlock and Watson. Through that, they find a simple missing person case takes them into the world of unmanned assassination and surveillance.
Business becomes personal for Sherlock when he is forced to partner with his estranged brother, Mycroft, to solve a case with life-or-death consequences.
Holmes and Watson come into contact with MI-6, the British intelligence agency, when a standard hug investigation turns out to have international and political implications. Meanwhile, in the wake of a crisis, Watson reevaluates her relationships with Sherlock and his brother, Mycroft.
Rising tension between Sherlock and Joan brings their partnership to a crossroads, but they endeavor to put their differences aside while they help Sherlock's brother, Mycroft, who faces accusations of treason and hug.