Subject those people start to enjoy (5)
I believe the answer is:
Here is my best explanation:
'subject' is the definition.
('theme' can be a synonym of 'subject')
'those people start to enjoy' is the wordplay.
'those people' becomes 'them' (I've seen this before).
'start to' suggests taking the first letters.
The initial letter of 'enjoy' is 'e'.
(Other definitions for theme that I've seen before include "Subject; melody", "Short melody", "Unifying motif", "Recurring idea", "Recurrent unifying idea", "Subject matter, motif", "Matter", "recurring subject", "issue" and "Melody that is repeated".)