Wrong Side of the Road (S05E15)

Holmes' former protégé, Kitty Winter (Ophelia Lovibond), returns to New York after a three-year absence to warn him that a killer is eliminating everyone involved with a case they worked on together in London, and they're the next targets. As Sherlock, Kitty, Joan and the NYPD join forces to find the perpetrator, Watson discovers Kitty has a life-changing secret. (CBS TV Network)