Roberston’s weighty tale is essentially a murder mystery in which her main protagonists, Harriet Westerman and Gabriel Crowther, move inside a highly restrictive code of 18th-century conduct. Walking a fine line between the socially acceptable if they are to survive, not only are Harriet and Gabriel both figures of considerable wealth and social standing, they’re also considered “flawed” in their desire to undertake grisly anatomical dissections of various murder victims.

Against a past involving the turbulent Jacobite Risings, Gabriel must confront the truth behind the execution of his brother, Lucius Adair, and the role that Lucius played in the murder of their father. In denial about the events leading up to Lucius's death, Crowther accepts an invitation for both him and Harriet to attend his former home of Silverside, a stately hall at Keswick in the Lake District. Crowther’s younger sister, Margaret “the Vizegrafin” von Bolsenheim, and her son, Felix, are staying as guests of the current owner, Mrs. Hetty Briggs. Apparently Hetty’s workers have found a desiccated corpse in a tomb on St. Herbert’s Island, and they want Crowther to help identify the body.

In Robertson’s tale of gothic horror, witchcraft, and murder, the picaresque hills surrounding Keswick are full of bloody histories. Harriet and Gabriel waste no time in pursuing their investigation. As Crowther places a scalpel to the mummified flesh of the corpse’s neck, Harriet--acknowledging that Gabriel has a an intimacy with the dead she does not savor--uses her considerable gifts for conversation, plunging herself into the world of the Gretas, the ancient kinfolk who once owned the land around Silverside years before Crowther’s family, the prestigious Pengaligons, bought the estate.

From the ruins of eerie Gutherscale Hall to truculent Felix’s accusations that Harriet and Crowther are intent to bring some new scandal to light that will further taint the family name, Robertson’s fabulous novel unfolds in tones as fresh and crisp as falling snow. Crowther’s father’s murder and his brother’s execution have haunted him for thirty years. As he finds himself caught between their mysteries and a series of new horrors, Harriet remains in desperate need after the recent loss of James, her beloved husband. Although Harriet already has a reputation for unconventional behavior, she can see that for so many men and women of her class, her actions only confirm her as yet another “oddity.”

When Harriet’s young son, Stephen, and his tutor, Mr. Quince, befriend earthy Casper Grace, a local apothecary, the result is a series of entanglements and disasters that touch virtually everyone with whom Stephen, Crowther and Harriet come into contact. Caspar is a fascinating personality: secretly plagued by the voices of a black witch, his actions circle the more mystical aspects of the narrative. With the light in his eyes and his thirst for the spaces and hills, the villagers consider Caspar a “cunning-man,” and his talk of grotesques, ghosts, and “the carvers formed from life” begin to take on a life of their own. Scenes involving Crowther’s boiling of bones--all for the dubious pleasure of driving fortune-hunters away from his unsympathetic sister--are contrasted with Harriet's verisimilitude and young Stephen's curious and enthusiastic sense of adventure.

Amid country manors, forests and towers straight out of a fairy tale, Robertson portrays many of her characters in brushstrokes both deep and broad, as well as filling them with considerable fault in an attempt to refract real emotion. Fresh from Mrs Briggs' garden party, another death shakes events up while Keswick’s magistrate perhaps knows more than he’s letting on. There are also the ministrations of kindly Miss Scales, the daughter of the vicar of Crosthwaite, who befriends Harriet and Stephen and whose skin on both her face and her hands is badly pitted with the scars of smallpox.

Perhaps the best in the series so far, there is subtle irony to Island of Bones as Crowther moves towards ameliorating the guilt that he probably allowed an innocent man to hang thirty years ago. Sensing how traditions and beliefs are dragged from one generation to the next, Robertson gorgeously layers Harriet and Gabriel's motivations with respect to the sensibilities, expectations, and moral strictures of the Victorian period.