All 3 Uses of

theme
in
Misery, by Stephen King

He remembered getting two letters suggesting Misery theme parks, on the order of Disney World or Great Adventure.†
Chpt 3 *

theme parks = amusement parks each of which have one or more basic underlying ideas -- such as the "Magic Kingdom" of Disneyworld

That first one had had all the life of an eighthgrader's 'How I Spent My Summer Vacation' theme.†
Chpt 2

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.)