Four individuals live in a secluded manor house in the English countryside and participate in an elaborate role‑playing fantasy called The Game. In The Game, each person adopts a role in a pretend 'happy' family, with the members known only by their assigned identities: Mumsy [Ursula Howells], Nanny [Pat Heywood], Sonny [Howard Trevor], and Girly [Vanessa Howard]. The rules of this ritual are strict but ill‑defined, with the principal one being Rule No. 1: Play the Game.
Within this world, the teenaged Sonny [Howard Trevor] and Girly [Vanessa Howard] regularly venture into populated areas, using Girly to lure men back to the manor as New Friends [Michael Bryant]. Those who refuse are sent to the Angels—a euphemism for ritual murders staged around playground games, which Sonny records on a 16 mm camera to create a private snuff film for the family.
One night, Girly [Vanessa Howard] and Sonny [Howard Trevor] attend a Swinging London party, where they meet a male prostitute and his latest client. An instant attraction grows between Girly and the man, who persuades his client to join the siblings for a night of carousing. The trio goes to a playground, where they murder the woman by throwing her from a large slide. The next morning, Sonny [Howard Trevor] and Girly [Vanessa Howard] convince the hungover man that he killed the woman after a night of heavy drinking, and they persuade him to return to the manor with them. The prostitute—rechristened New Friend [Michael Bryant]—is outfitted in schoolboy clothes and subjected to an indeterminate period of torment playing the game, during which he is repeatedly presented with his client's body as proof of the family's leverage over him.
After Mumsy [Ursula Howells] makes sexual overtures to New Friend [Michael Bryant] one evening, he begins to see an opportunity to turn the family against itself by creating sexual jealousy between the women after first sleeping with Mumsy and then Girly. Sonny [Howard Trevor], left out of the sexual politics, asks that New Friend be 'sent to the angels'; in a moment of panic, Girly [Vanessa Howard] bludgeons Sonny to death with an antique mirror. Chastising Girly for creating a mess, Mumsy [Ursula Howells] dismisses Sonny as 'naughty' and orders New Friend to bury Sonny beneath a drained fountain on the manor grounds, where makeshift gravestones bearing the numerical identities of the dispatched 'friends' mark the rows.
Nanny [Pat Heywood], jealous that she is the sole female left out of New Friend's attentions, attempts to murder Mumsy with acid‑tipped needles, but the attempt is interrupted by New Friend. Girly [Vanessa Howard], realizing Nanny's plan to target New Friend, hacks Nanny to death with an axe. In the kitchen, Mumsy [Ursula Howells] discovers Nanny's head cooking in a pot, and Girly [Vanessa Howard] sings:
> When she's dead, boil her head, make it into gingerbread
Mumsy and Girly declare a truce and decide to share New Friend by alternating which days of the week each may have him. Overhearing the arrangement, New Friend retrieves Nanny's acid‑tipped needles and, while lying on Mumsy's bed, hides them under the pillow.
