Watch The Ruling Class

Jack Gurney is the new Earl of Gurney. However, Jack sees himself as God, shocking friends and family by talking of rejoining the world to grant it love and charity, even breaking into song and dance. When his family challenges this identity, he places them within a "galvanized pressure cooker," never to be heard from again. Elsewhere, Jack's uncle, Sir Charles, weds Jack to his mistress, Grace, in hope of producing an heir and, in turn, a way to have Jack committed. However, Grace truly falls for Jack. Soon after, Lady Claire, Charles' wife, decides to make friends with Jack to spite her husband as well as sleeping around with Dr. Herder, Jack's psychiatrist, in order to expedite Jack's recovery.

Despite intensive therapy sessions, Jack's delusions are so powerful that he treats any contrary evidence as lunacy. On the night that Herder is to become a father, he tries one last treatment and introduces Jack to McKyle, a man believing himself to be Christ, or rather "The Electric Messiah," who uses electroshock therapy on Jack. Unable to rectify how two men could both be God, Jack's delusions of godhood shatter. Grace gives birth to a boy and Jack's delusions shift to perceiving himself as Jack the Ripper, proclaiming "I'm Jack, I'm Jack."

Charles sends for a psychiatrist to treat Jack. However, this doctor discovers that they have much in common, bonding with Jack and declaring him sane. Jack is able to hide his madness as needed but claims Claire as his first victim after she tries seducing him, successfully blaming the family butler. Later, Charles has a stroke and Dr. Herder's mind breaks upon discovering Jack killed Claire.

Jack takes his place within the government, offering a passionate speech toward punishments to wild applause. Come nightfall, Jack murders Grace after expressing her love to him. Her screams syncopate with their son's coos of "I'm Jack."