From the bestselling author of In the Blink of an Eye comes an inventive thriller that pits algorithms against experience, logic against instinct, and one undetectable killer against two extraordinary detectives.

"Unswervingly gripping and scary, and at the same time beautifully tender and humane."-Nicci French, author of Has Anyone Seen Charlotte Salter?

When the body of a man is found crucified at the top of a hill in the British Midlands, AIDE Lock-the world's first AI detective-and Detective Kat Frank are thrust into the spotlight as they are given their first live case. When a second body is found, the police issue an extraordinary warning to local males aged between thirty and forty years old:

• Avoid drinking in pubs.
• If you insist on going to a pub, do not leave alone.
• And definitely do not leave a pub with a stranger.

With the national media and local men in an uproar, Kat and Lock have to combine their instincts and algorithms to catch the killer before they can strike again.