Joan investigates her first solo case when a wife disappears. The missing woman left behind a tear-filled video that mentions a murder on a subway platform. While Joan searches for the vanished lady, Sherlock probes the murder.

While Kitty tries to find a runaway teen, Sherlock and Joan work a case in which the murder of a brilliant bioengineer looks to be at the hands of a drug cartel. Also, Joan makes a major life decision but worries it will impact Sherlock negatively, not knowing that Sherlock has big news of his own.