Morgan Delt is a working class artist with a Communist mother and a middle-class ex-wife. He is obsessed by gorillas - he visits them in the zoo, fantasises about them and identifies with them.
On the day that his wife Leonie divorces him, Morgan returns to their house, liberates his Marxist and gorilla ephemera from dust sheets, paints a hammer and sickle on the mirror, and puts a skeleton in the bed. Leonie takes out a court junction to bar him from the house, and he makes his home in her car outside.
Leonie is still susceptible to Morgan but she craves 'normality' and has a new man in her life, Charles Napier, an art dealer. Morgan goes to see him at his gallery, armed to the teeth, but Napier is unimpressed and throws him out. Undaunted, Morgan rigs up a tape machine in the house and plays a loud recording of a rocket launching when Napier next takes Leonie to bed. On another occasion Morgan manages to blow up his snobbish mother-in-law with a bomb under the bed.
Morgan's mother runs a café, to which he retreats now and then, and he accompanies her on the annual visit to Karl Marx's tomb in Highgate Cemetery, although she calls him a class traitor.
Leonie has the car towed away, but Morgan returns. He visits a psychiatrist, who considers him "a suitable case for treatment". In a moment of weakness Leonie goes to bed with Morgan, who fantasises that they are wild animals, mating. He wants her to have his baby, but Leonie is set on marriage to Napier and goes ahead with wedding plans.
Morgan and his mother's friend Wally, who is a professional wrestler under the name of 'The Gorilla', kidnap Leonie and take her to Wales, where they make camp by a lake. Morgan fantasises that he and Leonie are Tarzan and Jane, but Leonie is unmoved. Her father rescues her and Morgan is sent to prison.
Morgan is released from prison on the day of Leonie's wedding. He sees King Kong at the cinema, and hires a gorilla suit. Dressed in the suit, he gatecrashes the wedding, scaling the hotel walls like Kong. Chaos ensues, Morgan flees but the suit catches fire. Smouldering, Morgan steals a motorbike and drives into the river. He is washed up on a rubbish tip on the shore at Battersea. He cannot get the gorilla head off, panics and begins to hallucinate that everything he holds dear - his childhood ideals, his mother, Leonie - conspires with his enemies (Napier, mother-in-law) against him. He dreams that he is straitjacketed and shot by firing squad.
Morgan wakes up and is taken to hospital.
Leonie, pregnant, walks through a garden. It is the grounds of the asylum in which Morgan now lives. He is making a flowerbed in the shape of the hammer and sickle. Leonie tells him that the baby is his.
