Fresh from successfully closing their first live case, the Future Policing Unit are called in to investigate when a headless, handless body is found on a Warwickshire farm. But as they work to identify the victim and their killer, the discovery of a second body begins to spark fears that The Aston Strangler is back.

When DCS Kat Frank is accused of putting the wrong man behind bars all those years ago, AIDE Lock – the world's first AI detective – pursues the truth with relentless logic. But Kat is determined to keep the past buried, and when she becomes the target of a shadowy figure looking for revenge, Lock is torn between his evidence-based algorithms and the judgement of his partner, with explosive results.