Boyd goes back to the torture chamber and discovers that Nicholson is already there and admitting that he did indeed let the killer go all those years ago. Nicholson believes that Jason Heath is the responsible but Grace is not as convinced. Sarah ends up going missing as the investigation continues and after her car is found her friends grow more concerned. Boyd is instructed by Nicholson to remain focused on the M11 murders and he will investigate Sarah's disappearance. The team's suspicions about Nicholson increase.