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 investigate a murder that initially looks like a road rage incident, but takes a new direction when they learn the victim was flash-frozen at the time of death. Also, when Watson’s mother finds out Joan’s brother is cheating on his wife, she puts Joan in the awkward position of confronting him about the affair.
Holmes and Watson investigate the murder of a professional skeptic, a man who debunked paranormal, religious and scientific phenomena for a living. The case becomes urgent when his homicide reveals a potential threat to homeland security. Also, Captain Gregson’s daughter and fellow NYPD officer, Hannah, asks Watson for help with one of her cases.
Holmes and Watson look into the death of a member of Holmes’ online beekeeping community who was a researcher looking into a deadly Northeast honey bee outbreak. During the investigation, they meet Tara Parker, a brilliant entomologist, academic and the leader of New York’s beekeeping society. Also, Captain Gregson enlists Watson’s services in an off-book investigation that helps him make a life-changing decision.
As Holmes faces criminal charges in the aftermath of his recent violent behavior and relapse back into heroin, his position with the NYPD is put in jeopardy. Holmes concentrates on the case of a missing wife believed to have been killed by her husband to try to get back in the department’s good graces, while at the same time expecting a visit from his father.
When Morland offers to use his influence to have Sherlock and Joan reinstated as consultants to the NYPD, Sherlock’s mistrust of his father makes him question his motivation to help. Also, with no work offers coming in, Watson wrangles a gig with the FBI investigating a triple homicide in a top secret research lab.
When Sherlock finds himself distracted by his father’s ongoing presence in New York City, he offers to help Morland resolve a work issue in exchange for his prompt departure home. Also, Holmes and Watson’s investigation into the double murder of two men who looked alike leads them into the world of facial recognition technology.
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.
Holmes and Watson investigate a homicide in which the victim was murdered in a manner reminiscent of the crimes of an infamous, and already incarcerated, serial killer. Also, Sherlock and Joan tutor Detective Bell for a police sergeant’s exam that would lead to a promotion and a post at another precinct.
Sherlock and Joan search for a murderer who used poisonous mushrooms to kill a botany professor and a group of the instructor’s students. Also, when Joan is disturbed by loud noise next door, she discovers her neighbor, Trent, is renting out his home through a vacation site that caters to hard partiers.
At the urging of Morland’s wealthy associate, Henry Baskerville, Holmes and Watson look into the death of his brother and discover that a witness saw the man chased to his death by a large, glowing animal too fantastic to be real. Sherlock considers intervening when the trauma from the bombing at the morgue negatively impacts ME Hawes’ work.
A mysterious woman who organizes illegal, high-stakes poker games arrives on Holmes and Watson’s doorstep and tells them her life is in danger claiming to be a former associate of Mycroft, Sherlock’s brother. However, as the pair investigates, Joan becomes suspicious that their new client isn’t being truthful.
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. 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. 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 search for two murderers after a base jumper is shot out of the sky by one killer, and has his parachute sabotaged by another. 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.
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. 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.
In the conclusion, 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. Sherlock and Kitty’s relationship is strained after she shares life-changing news.
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. 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.
Holmes and Watson get mixed up in murder and magic when they investigate the death of a magician killed while performing a classic stunt. Also, Watson suspects Bell is being targeted by the ex-husband of his girlfriend, Chantal, after a false allegation lands him the middle of an Internal Affairs investigation.
When Detective Bell’s girlfriend, Chantal, is assaulted and her ex-husband is killed soon after, in what Holmes and Watson discover is a staged suicide, they search for one suspect behind the linked crimes. Also, as Bell fights the urge to seek his own brand of justice for Chantal, Sherlock makes a heartbreaking realization about the detective’s past.
As Holmes confronts a medical diagnosis that threatens both his career and sobriety, he meets Michael, a man who credits Sherlock for helping him conquer his own addiction. Holmes and Watson are hired by a reformed party girl heiress to find her missing partner in a years-old sex tape that has just leaked online.
Holmes and Watson race to help Detective Bell when he becomes a victim of a bio-terrorism attack at the precinct and the station is quarantined. During the lockdown, Captain Gregson and Detective Bell begin to suspect they are trapped inside with the perpetrator. Watson faces the difficult task of helping her mother, Mary, accept that her advancing Alzheimer's disease requires her to receive more medical care.
Holmes and Watson discover that the murder of a robotics engineer may be connected to his groundbreaking secret research in the area of real-life teleportation. Also, when Detective Bell is shut out of a required class he needs in order to complete his master's degree and join the U.S. Marshal Service, he is shocked to discover the course instructor has personal reasons for denying him access.
Sherlock's and Joan'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. As Joan grows increasingly homesick for New York, Gregson is wracked with guilt over his unresolved rift with his former consultants.
Sherlock 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. Joan helps the NYPD investigate a murder at a storage facility that caters to wealthy clients with items they want hidden from U.S. Customs.
An explosion at a traffic stop puts Sherlock and Joan on two separate tracks of investigation as they try to determine whether the attack was gang-related or a terrorist attack. Sherlock and Joan suspect there is more for them to discover regarding the recent attack on someone within their inner circle.
Tech billionaire Odin Reichenbach presents Sherlock and Joan with an extraordinary offer to help him with a program that can predict future crimes. Sherlock and Joan assist Bell when he tries to prevent a future crime of his own, as he races to locate a fellow NYPD officer planning a sniper shooting.
Sherlock and Joan receive a shocking request to collaborate from Reichenbach, who asks them to test his new crime prevention system. Tasked with investigating someone the program predicts will soon commit a crime, the duo worries Reichenbach will take drastic action before they conclude their inquiry.