All 3 Uses of

theme
in
Beastly, by Alex Flinn

The theme is darkness—people who live in darkness.
Part 3 *

theme = idea that is unifying or recurrent

In keeping with the invalid theme, there was a study off the bedroom with another plasma screen, just for the PlayStation.†
Part 3

Definitions:

(1) (theme as in: theme of the novel)
a basic idea that underlies what is being said or done -- especially in a literary or artistic work
(2) (theme as in: musical theme)
the initial or primary melody of a musical composition

or

(as in "theme song") music that is most repeated in a film, television series, or other theatrical production
(3) (theme as in: wrote a 2-page theme on my summer)
an essay written by a student

(This sense of theme is much rarer in recent decades than in the past.)