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.

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.

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.

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.

Watson considers a major life change after reading her own therapy file while she and Holmes investigate the murder of her former psychologist.