(In Manchester presentation some goons threw paper aeroplanes onto the stage.)
The play is set in a post-apocalyptic London, nine months after World War III ("the Nuclear Misunderstanding"), which lasted for two minutes and twenty eight seconds – "including the signing of the peace treaty". Nuclear fallout is producing strange mutations in people; the title refers to the character Lord Fortnum, who finds himself transforming into a bed-sitting room (other characters turn into a parrot and a wardrobe). The plot concerns the fate of the first child to be born after the war.
The film is set on the third or fourth anniversary of a war which lasted two hours and twenty-eight minutes. Three years after the nuclear holocaust, several survivors wander amidst the debris of London. Penelope is 17 months pregnant and lives with her lover, Alan, and her parents in the remains of the London Underground.
Other survivors include Capt. Bules Martin, who holds a "Defeat of England" medal, as he was unable to save Buckingham Palace from disintegration during the war. Lord Fortnum is fearful that he will mutate into the "bed sitting room" of the title. Mate is a fireguard, except that there is nothing left to burn. Shelter Man serves as a regional "head of government" over a decimated population. Similarly, the "National Health Service" is the name of a male nurse, although overwhelmed by the extent of the past war. Finally, there are two policemen who hover overhead in a balloon and shout "keep moving" to offset the 'danger' of becoming a 'target' in the (unlikely) event of another outbreak of hostilities.
Lord Fortnum travels to 29 Cul de Sac Place and does become a bed sitting room. Penelope's mother is provide with a death certificate, after which she turns into a cupboard. Penelope is forced to marry Martin because of his "bright future", despite her love for Alan. Her father is initially selected to become Prime Minister due to his prodigious leg length, but unfortunately, he mutates into a parrot and is cooked and eaten due to the starvation conditions that prevail.
Penelope finally gives birth, but her monstrous mutant progeny dies. It emerges that Martin is impotent, so he yields marriage consummation to Alan. Penelope has a second child, who is normal, and there is an indication of hope for the future amidst the devastation. She, Alan and her child walk off together. A band pays homage to Mrs. Ethel Shroake of 393A High Street, Leytonstone, the late Queen's former charwoman, and thus closest in succession to the throne.
The Bed-Sitting Room can be compared with Milligan's previous Goon Show, but with a savage, cynical and even more surreal edge, and an existential despair; one critic memorably described it as being "like Samuel Beckett, but with better jokes". It may have been in part, lampooning Aldous Huxley's pessimistic 1948 novel, Ape and Essence.