In October 1925, four New York City jazz musicians known as The Troubadours travel to the neo-Gothic Halcyon Castle near Gloucester, MA, home of occultist Duncan Fox, to perform a week-long series of entertainments. Halloween is Fox's fiftieth birthday and he's invited twelve family members and friends—including an astrologer, a tarot card reader, and a wizard—to celebrate with him.

The activities at Halcyon Castle, however, prove to be anything but what its name suggests. On the first night a Ouija board predicts the death of Fox's longtime friend Natalie Talbot from a heroin overdose. Her husband insists she never used drugs and suspects foul play.

Lizzie Crane, The Troubadours' beautiful and talented chanteuse, begins snooping into the unexplained death after local police place her and her colleagues under house arrest. She learns the deceased was a medium, who swindled many grieving people by pretending to communicate with their departed loved ones on the Other Side. Natalie Talbot also made enemies among some of the guests gathered at the castle. Soon the list of suspects grows to include the medium's lover, her cuckolded husband, and several others with vendettas to settle.

Natalie's death isn't the only mystery at Halcyon. The castle also has eerie voices emanating from its walls, a resident ghost, peculiar blinking lights, and secret passageways. As Lizzie pursues her quest into the strange goings-on, she discovers a plot to reap vengeance—and risks her own life in the process.