Watson starts her new job as an investigator for an insurance firm, but ends up joining forces on a case with Sherlock when a threat to Kitty emerges.
A Russian nuclear submarine disappears in American waters, putting Elizabeth in a tricky situation; Stevie ends things with her boyfriend.
Thomas Wilder, a serial killer, taunts Danny by attaching a note addressed to him to his latest victim.
Both sides of McCall's life converge when her daughter Delilah and her school friends are threatened by a European crime syndicate for being eyewitnesses to the outfit's execution of a drug cartel boss.