Plot
After a speech at a dinner proposing a toast to England, the 13th Earl of Gurney is got ready for bed by his butler Tucker. This includes setting up a silken noose above his four-poster, which the Earl uses for a bizarre autoerotic asphyxiation ritual. He survives this the first time, but it goes wrong the second time he tries it and kills him.
His half-brother Sir Charles, Charles' wife Lady Claire and their son Dinsdale gather to hear the reading of the 13th Earl's will. Three of the Earl's sons have already died overseas in the British Empire and the one survivor, Jack, is in a mental institution and thought to be unable to be present. He has been diagnosed as a paranoid schizophrenic prone to delusions of grandeur, caused or worsened by his time at boarding school, where he felt abandoned and victimized. As a subconscious defence against such abandonment, he developed a delusion that he was Jesus Christ returned to bring and embody love, so that people would have to love him in order to find peace and salvation.
The reading goes ahead - besides £30,000 left to Tucker and other bequests to eccentric charities, the relations are shocked to hear that the 13th Earl has left his title and estates not to Charles but to Jack, making him the 14th Earl. Jack arrives and asks for a moment of prayer, which actually turns into a conversation with himself, still thinking he is Jesus and God. Charles finds a loophole, that Jack can be sent back to the insane asylum so soon as he has married and begotten a sane heir to succeed him. However, Jack states he is already married, to La Dame aux Camélias, who he insists is a real person not a fictional character.
Charles has his long-time mistress Grace Shelly arrive in disguise as 'La Dame' and Jack agrees to her request for a 'second' wedding. This goes ahead, but Grace falls in love with Jack and becomes his ally. She also conceives a child by him, despite him spending their wedding night on a unicycle. Lady Claire also proves obstructive and begins an affair with Jack's psychiatrist Herder to try to persuade him to cure Gurney more quickly. Herder attempts to achieve this through intensive psychotherapy then - when this fails - resorts to shock therapy on the night that Grace goes into labour. This consists of bringing in another patient who also believed himself to be Christ, or, as the patient put it, "the God of electricity". Rather than drawing Jack to the conclusion that they cannot both be Christ, it causes him an apparent breakdown and he seemingly returns to his true identity as Jack Gurney.
Sir Charles, still intent on stealing the lordship, sends for a court psychiatrist to evaluate Gurney, confident that his nephew would be sent to an asylum for life. However, Jack puts up a front and plays on the psychiatrist being a fellow Etonian, getting himself declared sane. Jack also reveals to the audience that he has not been cured but instead switched to believing he is both the Old Testament God of vengeance and Jack the Ripper. Now a violent psychopath with a puritanical hatred of women, Gurney murders Sir Charles' wife in a fit of enraged revulsion when she tries to seduce him and frames Tucker (still working for the family) for the crime. Jack then assumes his place in the House of Lords with a fiery speech in favour of capital and corporal punishment. That night, Grace admits her love for him and he murders her for it.
