Great success, putting chapter into back story (5)
I believe the answer is:
eclat
'great success' is the definition.
(I've seen this before)
'chapter into back story' is the wordplay.
'chapter' becomes 'c'.
'into' is an insertion indicator.
'back' says the letters should be written in reverse.
'story' becomes 'tale' ('tale' can be a synonym of 'story').
'tale' back-to-front is 'elat'.
'c' placed inside 'elat' is 'ECLAT'.
'putting' acts as a link.
(Other definitions for eclat that I've seen before include "Loud applause" , "Brilliant display or effect" , "Brilliance" , "Ceremonial elegance and splendour" , "brilliant effort" .)