Episode 1 : The Past Is Parent
With Holmes facing criminal charges in the aftermath of his recent violent behavior and relapse, his powerful father Morland Holmes(John Noble) arrives in New York to fix his estranged son's troubles by any means necessary. Also, Holmes and Watson work the case of a missing wife believed to have been killed by her husband to try and get back in the NYPD's good graces.
Episode 2 : Evidence of Things Not Seen
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.
Episode 3 : Tag, You're Me
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.
Episode 4 : All My Exes Live in Essex
When Holmes and Watson investigate the murder of a fertility lab technician, they discover the woman had a secret personal life that leads them to multiple suspects. Also, the tables are turned on Watson when she's investigated by an NYPD detective.
Episode 5 : The Games Underfoot
When an archeologist is murdered, Holmes and Watson believe the man may have been killed for what he discovered during his last excavation in a local landfill. Also, Sherlock's relationship with Alfredo, his friend and former sobriety sponsor, hits a rough patch.
Episode 6 : The Cost of Doing Business
Morland offers to act as one of his son?s "Irregular" consultants so that he can lend Sherlock and Joan his considerable resources to help them solve a case.
Episode 7 : Miss Taken
When Watson's stepfather (John Heard) 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.
Episode 8 : A Burden of Blood
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.
Episode 9 : Murder Ex Machina
Holmes and Watson search for a computer hacker responsible for three murders, including the death of a Russian billionaire who was visiting New York City. Also, Joan is surprised to receive a solo dinner invitation from Sherlock's father.
Episode 10 : Alma Matters
Holmes' tentative reconciliation with his father suffers a setback when Holmes and Watson discover Morland has been keeping a secret that threatens all of their safety. Also, Holmes and Watson investigate two murders connected to a for-profit college and its illegal recruitment practices.
Episode 11 : Down Where the Dead Delight
Holmes and Watson must search for a killer without any physical evidence to aid them after a bomb is detonated in the New York City morgue. Also, Watson is suspicious when an NYPD detective she's in a grudge match with asks her to consult on a case.
Episode 12 : A View With a Room
Captain Gregson's colleague from Narcotics asks Holmes to orchestrate the perfect heist inside the heavily armed and virtually impenetrable compound of a drug-dealing biker gang. Also, when Watson assists Fiona Helbron (Betty Gilpin), who helped her on a recent case, she makes a surprising discovery about Holmes.
Episode 13 : A Study in Charlotte
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 (Richard Kind), is renting out his home through a vacation site that caters to hard pratiers.
Episode 14 : Who Is That Masked Man?
When Holmes' investigation into the attempt on Morland's life pushes their strained relationship to the breaking point, the identity of Sherlock's mother is revealed. Also, when three gang members are murdered, Holmes and Watson are amazed when an elderly woman emerges as their prime suspect.
Episode 15 : Up to Heaven and Down to Hell
When Watson runs into Captain Gregson and his secret girlfriend (Virginia Madsen), a former NYPD officer, she inadvertently sets the couple's breakup in motion. Also, Holmes and Watson investigate the murder of a wealthy woman who left her considerable estate solely to a beloved dog. Virginia Madsen guest stars.
Episode 16 : Hounded
At the urging of Morland's wealthy associate, Henry Baskerville (Tom Everett Scott), 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.
Episode 17 : You've Got Me, Who's Got You?
When a man who secretly fought crime dressed as a popular comic book superhero is murdered, Holmes and Watson must discover his real identity before they can find his killer. Also, Morland makes a surprise donation to Watson's favorite charity, in order to compel her to do him a business-related favor.
Episode 18 : Ready or Not
When a survivalist doctor goes missing, Holmes and Watson must determine whether he's purposely gone off the grid or if he's a victim of foul play. Also, Holmes exhibits odd behavior when his romantic relationship with Fiona (Betty Gilpin) hits a critical point.
Episode 19 : All In
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.
Episode 20 : Art Imitates Art
As Holmes and Watson investigate a woman's murder, they discover her death is linked to a piece of artwork that has ties to a crime that was committed when she was in college. Also, in the wake of a shocking personal revelation, Watson attempts to forge a connection with a recent client.
Episode 21 : Ain't Nothing Like the Real Thing
When Holmes and Watson are pulled into a double-homicide investigation, they discover the victims were staging a fake murder right at the moment they were killed. Also, Watson's inside man at Morland's office encounters a problem that threatens to expose her spying to Holmes and his father.
Episode 22 : Turn it Upside Down
Sherlock's father, Morland (John Noble), becomes Sherlock and Joan's prime suspect in a murder investigation after one of his employees is killed under the guise of a robbery.
Episode 23 : The Invisible Hand
When Holmes and Watson discover the perpetrator behind the attempt made on Morland's (John Noble) life, they find a shocking connection to themselves.
Episode 24 : A Difference in Kind
Holmes and Watson's lives are threatened by an influential, worldwide criminal network connected to the murder attempt on Morland Holmes (John Noble). Also, Sherlock's grievances with his father threaten their alliance to bring their mutual adversary to justice, on the fourth season finale.