Contains spoilers for this episode and earlier episodes.
At Jason Wilkie's execution, Lightman hears a denial that makes him doubt the conviction he helped obtain seventeen years earlier. Zoe prosecuted the case, and the possibility of an innocent man's death divides them. Soon, the threatening calls from the original kidnapping resume, and Oliver Sheridan disappears. Jason's brother Kevin threatens a lawsuit while the consultancy faces both financial exposure and the possibility that Lightman's judgment cannot be trusted.
An interview with Jason's former girlfriend produces the name Pied Piper, but her fear and Cal's efforts to reach her leave him briefly held in a psychiatric ward. The caller then threatens Emily, making Cal's pursuit intensely personal. Childhood photographs reveal that Kevin dominated his older brothers and played a clarinet. He made the calls and kidnapped the first victim, Rex, while Jason killed him. Their revenge began after their eldest brother died during the family's financial collapse.
Kevin abducted Oliver after Jason's execution to punish the Sheridans again. Cal and Reynolds search a stalled building project where Kevin worked and find Oliver alive behind a wall. Kevin attacks Cal, but is subdued and captured. Jason's denial of taking Rex was true without making him innocent of the murder. The investigation resolves that distinction after his execution, while Cal and Zoe have to live with the fear and uncertainty their earlier certainty brought back into their family.