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 murder.
Holmes and Watson come into contact with MI-6, the British intelligence agency, when a standard murder 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.
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.
When Sherlock’s brother Mycroft makes a surprise return to New York, his motivations cause discord between Sherlock and Joan. Meanwhile, a missing person case takes Sherlock and Joan inside the world of unmanned aeronautics.
A pickpocket dies of anthrax poisoning, putting Holmes and Watson on the trail of the toxin’s source in order to prevent more deaths.
A serial killer known for biting his victims appears to be killing again, even though he was presumed dead.
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.
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.
Tensions rise when Holmes and Watson are forced to partner with Gareth Lestrade, Sherlock’s former Scotland Yard colleague, on a bombing investigation.
Holmes’ latest investigation takes him inside a professional dance company when an up-and-coming ballerina is murdered. Meanwhile, Watson embarks on a solo enquiry to find a homeless veteran when his friend alleges he was abducted.
When Joan revisits one of Sherlock’s cold cases, she discovers an unsolved murder 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.
When a body is found in a barrel, Holmes and Watson launch an investigation into the mafia’s ties to the murder. Meanwhile, Sherlock attempts to make amends with Detective Bell.
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 hedge fund manager who was also running a Ponzi scheme is murdered, Holmes and Watson must determine which of his clients is guilty. Also, Sherlock contemplates sponsoring a fellow recovering addict.
When an investigation goes horribly wrong, Sherlock must testify in an official police inquiry which jeopardizes his and Watson’s future with the NYPD.
Holmes and Watson uncover the identity of a serial killer whose case has gone cold and find themselves butting heads with the NYPD.
When a beautiful young woman is murdered, Holmes and Watson investigate her ties to a billionaire CEO. Mycroft makes a case for Sherlock to move back to London.
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 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.
Holmes and Watson find themselves digging through the dark world of the mob to find a killer 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 a financial consulting company CEO is poisoned to death, a woman from Sherlock's past emerges as a possible suspect.
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 a well-respected mathematician is found dead, Holmes and Watson set out to solve a murder 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.
Holmes and Watson travel to London to help track down an old mentor and investigate an unsolved mystery. Meanwhile, Mycroft Holmes, Sherlock's estranged brother, reunites with Sherlock and reveals some secrets of his own.
