Episode 1 : Step Nine
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. Rhys Ifans guest stars.
Episode 2 : Solve for X
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. Jeremy Jordan guest stars as Joey Castro, the son of Watson's former patient.
Episode 3 : We Are Everyone
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. Tony Award winner Steve Kazee guest stars.
Episode 4 : Poison Pen
When the CEO of a financial consulting company is poisoned to death, Holmes and Watson are called upon to track down the killer. Meanwhile, a woman from Sherlock's past emerges as a possible suspect. Laura Benanti guest stars as Anne Barker.
Episode 5 : Ancient History
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.
Episode 6 : An Unnatural Arrangement
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. Talia Balsam guest stars.
Episode 7 : The Marchioness
Sherlock's brother, Mycroft, arrives in New York and enlists Holmes and Watson to help solve a case involving his former fiancee. Meanwhile, Sherlock has a difficult time accepting Mycroft and Joan's relationship. Rhys Ifans guest stars.
Episode 8 : Blood Is Thicker
When a beautiful young woman is murdered, Holmes and Watson investigate her ties to a billionaire CEO. Meanwhile, Mycroft makes a case for Sherlock to move back to London. William Sadler, Margaret Colin, and Rhys Ifans guest stars.
Episode 9 : On the Line
Holmes and Watson uncover the identity of a serial killer whose case has gone cold and find themselves butting heads with the NYPD.
Episode 10 : Tremors
When an investigation goes horribly wrong, Sherlock must testify in an official police inquiry which jeopardizes his and Watson's future with the NYPD.
Episode 11 : Internal Audit
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.
Episode 12 : The Diabolical Kind
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. Natalie Dormer Returns as Moriarty.
Episode 23 : Art in the Blood
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. Rhys Ifans returns as Mycroft Holmes.