Sherlock returns to New York with a new apprentice and a renewed interest in working with the NYPD after being fired by London’s MI6. However, Gregson won’t let him resume consulting for the department without permission from his former partner, Joan, the NYPD’s new go-to private investigator.

When Sherlock and Joan join forces on a double homicide, Sherlock’s new apprentice threatens the investigation when she allows her jealousy of Sherlock and Joan's work rapport to override her better judgment.

Sherlock helps a math genius from his network of 'Irregulars' experts after he stumbles upon a body while participating in a math puzzle competition. Joan attempts to extend an olive branch after she learns about Kitty’s past.

Sherlock takes on the case of a stolen artificial intelligence software program, but seeks out Joan when he'd rather disprove the computer's abilities than find the thief. Joan meets Sherlock head-on when she finds out he's met with Andrew without telling her.

Holmes and Kitty investigate the murder of a postal store owner whose death is connected to the illegal diamond trade. Meanwhile, Gregson's career is placed in jeopardy when he hits a fellow NYPD officer.

Holmes and Watson search for a thief who committed murder to steal a rare map. Meanwhile, Watson becomes concerned with Sherlock’s escalating interference into Kitty’s burgeoning personal life.

A bored Sherlock forces his investigative services onto Joan, who is trying to locate a woman who has been missing for five years, and the only clue is the smell of nutmeg at the site of her disappearance. Meanwhile, Joan’s bond with her long-distance boyfriend, Andrew, is tested when a man from her past reappears and asks for her help.

Holmes and Watson join forces with the NYPD after a police officer is murdered. Also, Sherlock searches for the creator of a “recovery blog” who is posting personal statements he has made in sobriety meetings.

When Watson joins forces with Holmes and Kitty to locate a missing nurse she used to work with, the woman’s trail leads them to another person who has recently disappeared.

While Kitty tries to find a runaway teen, Sherlock and Joan work a case in which the murder of a brilliant bioengineer looks to be at the hands of a drug cartel. Also, Joan makes a major life decision but worries it will impact Sherlock negatively, not knowing that Sherlock has big news of his own.

Watson begins her new job as an in-house investigator for an insurance firm. However, her attention shifts to a case that is personal for both her and Holmes when they join forces to eliminate an imminent threat to Kitty.

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’ 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.

Joan and Kitty try to prove that a string of murders, stemming from an old case Sherlock and Kitty solved in London, is connected to an international government conspiracy with the Defense Intelligence Agency at its center. Also, Sherlock and Kitty’s relationship is strained after she shares life-changing news.

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.