When Mother Dorothy, Prioress of the Order of the Daughters of Compassion, inherits a considerable estate from her godmother, Louisa Cummings, nobody would guess that the death of the old lady will lead to one of Sister Joan's most dangerous and puzzling cases yet. Linked with the mysterious death are an apparent suicide and the disappearance of an abused child. In the local hospital suspicion and fear stalk the wards and, in the convent high on the Cornish moors, that fear is reflected—for someone is watching and waiting. With the help of her friend Detective Sargeant Mill, Sister Joan sets out to trap one of the most dangerous of killers, and in the process discovers the true nature of compassion.