When DI Rowan Jackman and DS Evans are told that the IT boss has disappeared, they soon suspect foul play. Orla Cracken, known as Orac, is no ordinary techie, she was once a field agent travelling abroad undercover, working for the government.

Meanwhile DC Robbie Melton discovers that two people, both urban explorers, have mysteriously disappeared whilst out exploring abandoned buildings. One went missing at a disused airfield, but was it a military base, or was it civilian?

The gruesome discovery of their decaying bodies found hanging in ancient church ruins bursts the case wide open, and Jackman and Evans are under pressure to find the killer. With Orac safely back in the picture following a secret journey to Ireland to try and find her long-lost sister who went missing as a child, the hunt is now on to find the killer before he hangs his next victim.

It soon becomes clear that the killer is targeting urban explorers, but why is he determined to track down and torture these innocent people, and how is the case connected to Orac’s mysterious past, still shrouded in secrecy?