His novels, the first of which was published in 2005, are often dark and quirky takes on family life. The Last Family in England tells the story of Shakespeare's Henry IV, Part 1 with the protagonists as dogs. It was a best-seller in the UK and the film rights have been sold to Brad Pitt's Plan B production company with Taika Waititi directing. His second novel Dead Fathers Club is based on Hamlet, telling the story of an introspective 11-year old dealing with the recent death of his father and the subsequent appearance of his father's ghost. His third adult novel, The Possession of Mr Cave, deals with an obsessive father desperately trying to keep his teenage daughter safe. His children's novel, Shadow Forest, is a fantasy that begins with the horrific death of the protagonists' parents. It won the Nestlé Children's Book Prize in 2007. He followed it with the sequel, Runaway Troll, in 2008. Haig's vampire novel The Radleys, was published in the summer of 2011. A film adaptation of The Radleys has been announced, with Alfonso Cuarón attached to produce. Published in 2013, The Humans is the story of an alien who takes the identity of a university lecturer whose work in mathematics threatens the stability of the planet who must also cope with the home life which accompanies his task. The novel is in part an examination of mental illness and how those who suffer can become isolated.