Holmes and Watson face their greatest challenge to date when a murder investigation threatens to destroy their partnership.

When Watson’s stepfather writes a crime novel based on her work with Holmes without her knowledge, an underlying issue in their relationship is revealed. Also, as Holmes and Watson investigate a retired FBI agent’s murder, they discover the man’s death is connected to an unsolved case from the victim’s career.

Amidst Holmes and Watson’s battle with tech billionaire Odin Reichenbach, the investigators receive word of their old enemy and Sherlock’s former love, Jamie Moriarty.

As Sherlock reels at the reappearance of his former lover, Irene Adler, a series of flashbacks unravel the tumultuous events that led to his downfall into addiction. Meanwhile, he and Joan once again find themselves in the crosshairs of the enigmatic Moriarty.

Sherlock is reunited with “M.” a British criminal who appears to have followed Sherlock to New York. Meanwhile, Joan has reservations about leaving Sherlock and taking on a new client.

As Sherlock reels at the reappearance of his former lover, Irene Adler, a series of flashbacks unravel the tumultuous events that led to his downfall into addiction. Meanwhile, he and Joan once again find themselves in the crosshairs of the enigmatic Moriarty.

As Kitty begins to unravel due to the imminent threat to her safety, Sherlock and Joan intensify their efforts to help her. Also, the origin of Sherlock and Kitty’s relationship is revealed.

Holmes and Watson join forces with Holmes’ father, Morland, to enlist his vast criminal network to help disassemble tech billionaire Odin Reichenbach’s crime prevention system.

Tech billionaire Odin Reichenbach inadvertently provides Holmes and Watson with a lead that could give them evidence that brings him to justice.

Sherlock agrees to take a case from a man claiming to be Moriarty, hoping it will bring him closer to finding his nemesis. Meanwhile, Gregson encourages Joan to give up the dangerous line of work she has chosen and go back to being a sober companion.

Sherlock resumes his hunt for Moriarty when Sebastian Moran reveals that a man who was thought to be dead from a heart attack was actually on the list of intended victims from Moriarty.

Holmes and Watson find themselves on the hunt for a serial killer after a murder rocks their inner circle. Also, Holmes’ neurological recovery regresses and his sobriety wavers as his commitment to catching the killer grows into an obsession.

Holmes and Watson’s new careers as consultants for Scotland Yard in London take them inside the tabloid journalism industry when a popular model is the victim of an acid attack. Also, as Watson grows increasingly homesick for New York, Captain Gregson is wracked with guilt over his unresolved rift with his former consultants.

Holmes and Watson try to work a stateside investigation from London when someone close to them is gravely wounded by an unknown perpetrator in the United States. However, Holmes’ stateside legal trouble – the result of a confession to a murder he didn’t commit – threatens to derail their efforts.

Tech billionaire Odin Reichenbach hires Holmes and Watson to investigate a personal threat he suspects originated from within his own company; Holmes and Watson search for a motive behind three seemingly unconnected murders.

Holmes and Watson work to determine if a long dormant serial killer has resurfaced in the wake of a sculptor’s murder in New York City. Also, Watson suspects Holmes is keeping something from her regarding tech billionaire Odin Reichenbach.

Sherlock investigates what he believes will be an open-and-shut case after Detective Bell is attacked. However, the case takes an unexpected turn when the suspected assailant is found dead. Meanwhile, Sherlock encourages Joan to learn self-defense.

When Holmes and Watson discover the perpetrator behind the attempt made on Morland’s life, they find a shocking connection to themselves.

Holmes and Watson’s deadly conflict with Sherlock’s former friend Michael intensifies when their newest victim looks to be the serial killer’s latest prey.

Holmes takes extreme measures to secure his return to New York when he leans on his father’s disreputable connections to aid his legal re-entry into the United States. Also, while Holmes looks for a way back to the United States, Watson helps the NYPD investigate a murder at a storage facility that caters to wealthy clients with items they want hidden from U.S. Customs.

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 take on an investigation of a personal nature when Holmes’ recovery sponsor, Alfredo, suddenly disappears. As they delve into Alfredo’s life for clues, Holmes questions whether their friend has been abducted, or worse, if he suffered a relapse into addiction.

Captain Gregson’s colleague from Narcotics asks Holmes to orchestrate the perfect heist inside the heavily armed and virtually impenetrable compound of a drug-dealing biker gang. Also, when Watson assists Fiona Helbron, who helped her on a recent case, she makes a surprising discovery about Holmes.

Holmes and Watson’s lives are threatened by an influential, worldwide criminal network connected to the murder attempt on Morland Holmes. Also, Sherlock’s grievances with his father threaten their alliance to bring their mutual adversary to justice.

Holmes’ former protégé, Kitty Winter, returns to New York after a three-year absence to warn him that a killer is eliminating everyone involved with a case they worked on together in London, and they’re the next targets. As Sherlock, Kitty, Joan and the NYPD join forces to find the perpetrator, Watson discovers Kitty has a life-changing secret.