A girl, Ally Macready, surprises two campers, babbling that the Tall Man has taken her two friends. This case will take JJ back to her hometown, East Allegheny, a place to which she swore she would never return. Ally tells Lewis and Alves what she remembers about the Tall Man. Ally has early-onset schizophrenia. Chelsea's dad Tom tells JJ she and Bethany were going to talk to Ally about getting some help. Brandishing a razor, the Tall Man keeps asking the captive girls "Where is it?," referring to their innermost secrets. All three girls' phones were laced with fentanyl. JJ finds out Bethany had a secret boyfriend and Chelsea is determined to find out who it is. JJ keeps flashing back to her late, older sister Rosaline and her suicide. Ally gives the team more details, which allows JJ to figure out where they are, an abandoned train car. Bethany set up the whole Tall Man scenario with her boyfriend. She stabs Chelsea, but Alves and JJ find her in time. Chelsea reacts to the heart necklace around JJ's neck, which Rosaline gave to her. Then JJ determines the necklace is the unsub's trophy. They suspect Chelsea's dad Tom, who overlaps with both Roslyn and Bethany. But he doesn't react to the necklace, and JJ says he's not the one. Rossi points out that the unsub had to have been in JJ's life, so she needs to comb her memories. Rosaline gives JJ the necklace to ward off real monsters. Rossi asked who looked at her with fear in his eyes, and she settled on Ethan Howard, the principal, who attacks Bethany at the school. JJ interrogates Howard. He hints at where Bethany is  JJ saves her with chest compressions. WIll gives JJ a locket with their boys' pictures inside.