At twenty-eight, Hermann Horst is the youngest professor of philosophy to grace the marble corridors and richly paneled lecture halls of Austria-Hungary's esteemed University of Vienna. The charismatic young professor's success has been driven in part by personal tragedy: the mysterious death of his only sister. Her fatal obsession with divination and the occult has placed Hermann on a course to scientifically and logically explain the psychology of the occult and those who believe in supernatural powers. The university affords Hermann the resources needed for his research, albeit under the guise of his sanctioned academic coursework.

When a letter arrives from Senior Inspector Orczy Géza of the Budapest Gendarme asking for Hermann's help in a murder investigation, Hermann jumps at the opportunity to put his research into practice. The investigation centers on Schattenturm, Shadow Tower in German, an extravagant Neo-Gothic estate built atop the ruins of a medieval fortress. The body of the estate's gardener was found with an ancient war hammer lodged in the back of his skull, at the center of the swirling maze that surrounds the castle's mausoleum. Géza's investigation has been stalled by superstition surrounding the castle: a legend that ghosts and the devil are at work to drive out the family who recently acquired Schattenturm. A convenient story to assist a murderer perhaps, but one that has derailed Géza's efforts all the same. Géza is a no-nonsense veteran of conflicts in Bosnia, but he's at his limit with this investigation and he'll have to learn to trust and confide in Hermann's mentalist methods and knowledge of the occult if the investigation, and his career, are to be saved.

The current owners of Schattenturm, the Baum family, acquired the castle under unscrupulous circumstances after establishing a coal mine in the town nearby that exploits the locals and robs the countryside of its peace and beauty. The displaced aristocratic owners, the von Voitsbergs, are still very much a factor in the estate's realm. Hundreds of years of ownership and rule over the area are not easily forgotten, nor has the loss of their dark romantic home been amicably accepted. A handful of long-term servants know everyone's secrets and are willing to take them to the grave, though not necessarily to their own.

What lies beneath the black stones of Schattenturm, from the catacombs of the von Voitsberg crypt to terrible acts kept secret for decades, has destroyed lives. The secrets uncovered and the nature of the victim will shake Hermann and the readers, forcing them to question the morality of murder itself and whether some crimes should ever be forgiven.