When a serial bomber becomes active again after being dormant for six years, Watson seeks help from Shinwell Johnson, a former patient whose life she saved when she was a surgeon. Also, Holmes senses Watson is unhappy and questions whether she is still fulfilled by her detective career.
When the leader of a local street gang abducts Holmes to compel him to find the person responsible for a hit on his men, Holmes and Watson get caught in the middle of an international hunt to recover a centuries old, priceless artifact. Also, Watson debates whether a personal favor Shinwell asks of her is outside her comfort zone.
Captain Gregson lobbies to include Holmes and Watson when his unit is selected to receive a city commendation for its exemplary work. Also, as Holmes and Watson consult on the investigation into a financial analyst's murder, they are drawn into the world of asteroid research.
Holmes and Watson have plenty of suspects when they investigate the murder of a man who led a secret life as a vigilante, "catfishing" sexual predators on dating sites and publicly shaming them. Also, when Shinwell's criminal record prevents him from finding a full-time job, Holmes disagrees with Watson's plan to help him.
Holmes and Watson investigate a mass murder when a chef and his patrons are poisoned after dining on a tasting menu tainted with snake venom. Also, Detective Bell's crush on a work colleague makes Holmes realize his and Fiona's relationship is at an important crossroads.
Holmes and Watson search for two murderers after a base jumper is shot out of the sky by one killer, and has his parachute sabotaged by another. Also, after Joan's sister, Lin, thinks she sees Shinwell with a member of his old gang, Joan takes drastic measures to make sure he won't be drawn back into a life of crime.
Joan worries Sherlock's sobriety is at risk when she learns he has been lying to her about attending recovery meetings. Also, Sherlock and Joan discover a man's death caused by ingesting poisoned sausage is connected to a lab working on a breakthrough in the artificial meat industry.
Holmes and Watson race to find a woman who's been held captive for years before the kidnapper takes drastic steps to avoid being caught. Also, Watson becomes frustrated when Shinwell refuses to focus on his informant training with her and Holmes.
When Holmes and Watson investigate a clown's murder upstate, they discover a connection between his death and the creation of a new weaponized virus. Also, Watson helps Bell when he's targeted by his new love interest Chantal's ex-husband in attempt to sabotage her career at the district attorney's office.
A man takes hostages, including Joan, and threatens to execute them unless Holmes finds the person responsible for the death of his son. As Sherlock investigates, the captor gives him 16 hours to find the perpetrator before the statute of limitations on the crime runs out.
Holmes and Watson investigate the murder of a former professional eSports video game player who died after being assaulted in front of his fans during a live video stream. Also, Shinwell approaches Joan for advice when his teenage daughter asks to meet with him for the first time in years.
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.
The police call in Holmes and Watson to consult on a homicide "heard" by a cutting edge gunshot detection system when they can't find any tangible evidence that a crime was committed. Also, Sherlock and Joan become suspicious of Shinwell when he's the target of a drive-by shooting that reveals a connection between him and an unsolved murder.
Sherlock and Joan question how well they know Shinwell when they investigate the possibility he may have gotten away with the unsolved murder of his friend, a fellow gang member. Also, Sherlock and Joan's latest case puts them on the hunt for a treasure map rumored to lead to a fortune in pirate's gold hidden around New York City.