Luther returns to work after a traumatic arrest to investigate the murder of a former child genius's parents, and quickly deduces that their daughter is responsible. However, unable to find evidence to convict, he becomes embroiled in a battle of wits with the suspect - who has set her sights on him and his estranged wife.

A gunman begins murdering uniformed police officers, prompting the detective to taunt the killer on TV in the hope of inspiring him to turn his anger on him and come out into the open. To his horror, Luther also learns that Alice Morgan has been investigating his past - and is threatening to tell Zoe what she has discovered.