Sherlock and Kitty investigate the murder of a small postal store owner whose death is connected to the illegal diamond trade. Also, Captain Gregson puts his career in jeopardy when he hits a fellow NYPD officer.

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.