Twelve years after sixteen-year-old Joanna Gold famously disappeared in broad daylight on Hampstead Heath, the dress she was wearing is found in a lock-up garage owned by one of her old friends. Suspecting that he may have been responsible for her death, and having discovered blood on the dress, Boyd is convinced he has found his man. However, when evidence points to another assailant, he is forced to let his original suspect go - which later results in a suicide attempt. Feeling guilty that he persecuted the wrong person, Boyd goes on a manhunt in order to discover the real identity of her killer. When Joanna's sister, Clara, informs Boyd that she is being followed, he suspects that the killer is going to strike again, and uses Clara as bait to lure him out. However, while under pressure to keep a watchful eye, Boyd slips up and makes possibly some irreversible mistakes, leading to Clara's father informing the Chief Constable of Boyd's actions. Realising the mystery of Joanna's murder lies closer to home than first thought, Boyd uses cunning tactics to flush the killer out.