A Plague of Pythons is a science fiction novel by American writer Frederik Pohl. Serialized in Galaxy Science Fiction in October and December 1962, the novel was published in 1965, and an updated version was published in 1984 under the title Demon in the Skull. The title derives from the words "Domina Pythonis" used as part of an exorcism ritual performed in the first chapter to scare away the "demons" that seem to possess people in the novel. The novel opens in a world reduced to a grim struggle for existence after a plague of madness that afflicted individuals at random. Some two years previously, every government in the world was attacked by its own military machinery, which then self-destructed. All civilian air transport was similarly destroyed, along with major cities like San Francisco. After the initial meltdown, people began claiming to be "possessed". They would commit crimes of violence, but afterward they would claim to have had no control over their actions. This leads to superstitions about demonic possession, as well as a novel legal defense.