The film is based on Philip K Dick’s 1968 novel Do Androids Dream of Electric Sheep?, and is set in Los Angeles. The 'hero' is a detective called Deckard (expertly played by Harrison Ford), who hunts down androids – in the film they are called replicants – who have escaped from their slave jails on outer-space colonies and are trying to blend in back on Earth. Rutger Hauer's android Roy Batty is one of the most dangerous, yet appealing, 'monsters' in cinema.