When the newspapers turn up to cover Ruby Bright's 100th birthday, they find her seaside care home is a murder scene. Someone spirited Ruby away by wheelchair down to the water's edge on the idyllic north Norfolk coast, and strangled her. But why kill a harmless centurion?

As Detective Inspector Shaw and Detective Sergeant Valentine investigate, it's clear Ruby wasn't the first victim, and nor is she the last. All trails seem to lead back to the old Parkwood Springs estate, close to the docklands. There's only one way in and one way out of the estate - through the derelict Lister Tunnel. But what is the secret within ...?