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.
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 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 (Samantha Quan), 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 (Chasten Harmon) ex-husband in attempt to sabotage her career at the district attorney's office.
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, on the conclusion of a two-part.
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.
Watson and Holmes search for the suspect believed to be behind both the assault on Chantal, and her ex-husband's staged suicide; Bell fights the urge to seek his own brand of justice for Chantal; Sherlock makes a heartbreaking realization about Bell.
After a reality show contestant is killed, another competitor becomes the leading suspect. He's a former war criminal who may be the most skilled killer that Holmes and Watson have ever pursued. Shinwell reappears and asks Joan for a favor.
Holmes and Watson pursue an elusive criminal as a gang war erupts in New York City. While the NYPD works to contain the violence, the two investigate the murder that appears to have ignited the city-wide conflict and discover that a familiar face is pulling the strings.