"A Head Full of Ghosts" is a psychological horror novel by Paul Tremblay that explores themes of mental illness and the nature of belief. The story follows the Barrett family, particularly Marjorie Barrett, a teenager who exhibits signs of possession, leading to a reality show that documents their struggles. The narrative is presented through the perspective of Meredith Barrett, Marjorie's younger sister, who reflects on their past and the impact of the media on their lives. The novel blurs the lines between reality and fiction, raising questions about the authenticity of experiences and the influence of societal perceptions.