Holmes returns to New York with a new apprentice and a renewed interest in working with the NYPD after being fired by London's MI6. Unfortunately, Joan, the NYPD's new go-to PI, must give her approval first.

When Holmes and Watson join forces on a double homicide, Sherlock's new apprentice, Kitty, 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. Meanwhile, Joan attempts to extend an olive branch after she learns about Kitty's past.

An A.I. computer is suspected for the murder of its creator; Sherlock and the team go to work to solve the case.

Sherlock and Kitty investigate after a man's severed hand is found in the street; Gregson gets in trouble with the brass and his daughter when he punches another cop; Sherlock discovers a manuscript that Watson has written about his cases.

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.

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.

Watson starts her new job as an investigator for an insurance firm, but ends up joining forces on a case with Sherlock when a threat to Kitty emerges.

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 are faced with a very large suspect pool when a debt collector is murdered; Andrew wants Watson to meet his father.

Sherlock and Detective Bell investigate the kidnapping of two zebras from the zoo.

Holmes investigates himself when he becomes a suspect in a murder that took place during the height of his addiction; clues make Holmes question his innocence.

A murder victim turns out to have been instantly frozen at the time of death; Watson is forced to have an awkward conversation with her brother after learning he is having an affair.

A driver for a ride sharing company is intentionally run over by a city cab, Sherlock and Joan wonder if it's a case of professional jealousy. A romance Sherlock has with a longtime Irregular complicates when she makes a shocking request.

Holmes and Watson are drawn into an Internet war when a member of the everyone hacker group is murdered.

A researcher - one of Sherlock's fellow beekeepers - who was investigating a deadly honeybee outbreak is killed; Capt. Gregson asks Watson for help with an unofficial investigation that helps him make a decision.

Holmes and Watson take on an investigation of a personal nature when Holmes' friend and former recovery sponsor, Alfredo, disappears under suspicious circumstances.