Plagued by recurring nightmares since childhood, Jessica has begun studying the psychophysiology of dreams in an attempt to understand their meaning. When her Grandmother dies, Jessica returns to the family home in the French countryside, where she receives a muted reception from her icy Mother, Catelyn. After a difficult first night, Jessica becomes feverish and uses her bedridden state to practice lucid dreaming. Family secrets run deep, and Jessica discovers that her Grandmother committed suicide after becoming obsessed with the same horse-headed apparition that frequents her nightmares. Her skills as a lucid dreamer improve and her visions reveal secrets about her past that her Mother has kept from her, all the while leading her to confront the monstrous Horsehead.