The Skull Beneath The Skin by P. D. James

A young private investigator is hired to protect a celebrated actress who has been receiving sinister, literary death threats ahead of a weekend performance at a restored island castle. When the actress is murdered, the detective must sift through a closed circle of friends, rivals, and lovers to expose old betrayals and concealed motives. The investigation peels back layers of theatrical illusion and personal deceit, culminating in a chilling unmasking of the killer.

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