Illegitimacy versus legitimacy: Nora and Dora are from "the wrong side of the tracks" and were "born out of wedlock", their father is "a pillar of the legit theatre" and throughout the book the twins are constantly trying to become legitimate and be accepted. However, Carter questions the concept of legitimacy, and whether it is just a perception rather than reality: even the characters that are seen to be from the legitimate side do not always act in a respectable way, for example Saskia has an affair with Tristram, her half-brother. See Illegitimacy in fiction.
Carnivalesque: Carter uses the carnivalesque to illustrate some of her points about social boundaries, such as illegitimacy and highbrow/lowbrow. Important instances include the scene at the burning mansion in Chapter 2, where she describes the "orgiastic" element to the scene, using images of the "flickering flames" to emphasise this: the highbrow party and mansion is reduced to a ruined, passionate near-orgy by the fire and the breaking of social boundaries. This is similar to the final chapter when Dora and Perry have sex, as Nora says she wishes Dora would "fuck the house down": as well as physically damaging the Hazard residence, Dora and Perry having sex almost brings down the divide between the highbrow and lowbrow sides of the family. Some of the imagery used in this scene echoes the imagery of the Chapter 2 scene, for example "cover them all... with plaster dust and come and fire".
Incest: for example Saskia and Tristram are half brother and sister (although may be cousins), Nora loses her virginity to a pantomime goose when playing a gosling, Perry sleeps with Dora. Melchior and Peregrine also share partners (e.g. Daisy Duck, Lady A); Nora and Dora both sleep with the Blond Tenor. This could be seen as carnivalesque, as it inverts social hierarchies and boundaries. There is also the recurring idea of the actress playing Cordelia falling for the actor playing Lear in Shakespeare's "King Lear" on stage.
Culture and class: the high culture of the theatre in the legitimate side of the family as opposed to the dance halls in which Nora and Dora perform.
Shakespeare: Shakespeare is used continually, the ideas of his plays are incorporates, comparisons made continually between characters of the book and of the play and the book itself is written in five chapters just as a Shakespearian play often had five acts. Melchior idolises his father, and also Shakespeare, worshipping earth from ground that Shakespeare once performed on more than his own daughters. The inclusion of Shakespeare references in Dora's narrative highlights the idea of culture and class and of Shakespeare now being considered "high art".