In the ninth Ruth Galloway mystery, Ruth and Nelson investigate a string of murders and disappearances deep within the abandoned tunnels hidden far beneath the streets of Norwich.

Norwich is riddled with old chalk-mining tunnels, but no one's sure exactly how many. When Ruth is called in to investigate a set of human remains found in one of them, she notices the bones are almost translucent, a sign they were boiled soon after death. Once more, she finds herself at the helm of a murder investigation.

Meanwhile, DCI Nelson is hunting for a missing homeless woman,...