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. Also, 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.
Watson and her half sister, Lin, have conflicting reactions when their estranged biological father dies. Also, Holmes and Watson find themselves on the hunt for a stolen plutonium shipment they fear will be used to make a dirty bomb after a Department of Energy inspector is killed with a lightning gun.
Holmes and Watson enter the world of rare antiquities when they investigate a case in which the victim was killed during a Revolutionary War reenactment. As Holmes grows frustrated with the length of his cognitive recovery, he finds solace in his growing friendship with Michael.
Holmes' former sobriety sponsor asks for help with an illegal endeavor in order to save his brother. Holmes and Watson investigate the poisoning of a biology professor who was working on a secret project.
Sherlock and his father attempt to repair their strained relationship upon learning of a death within their family. Holmes and Watson discover a link between their latest case and the world of Egyptian antiquities.
Holmes engages an old foe to protect his father, Morland. Holmes and Watson search for a killer connected to the tobacco industry when a lawyer, who was reviewing a major cigarette distributor's finances, is murdered.
Detective Bell considers leaving the NYPD after he is recommended for a once-in-a-lifetime career opportunity. Holmes and Watson investigate the disappearance of a young woman who led a double life as a financial dominatrix.
It's a race against time for Holmes and Watson when Detective Bell becomes a victim of a bioterrorism attack at the precinct. During the quarantine, Gregson and Bell suspect they are trapped inside with the terrorist.