Rip into first six chapters then the MS (6)
I believe the answer is:
script
'the ms' is the definition.
(thesaurus)
'rip into first six chapters then' is the wordplay.
'into' is an insertion indicator.
'first' says to take the initial letters.
The first letters of 'six chapters then' is 'sct'.
'rip' put inside 'sct' is 'SCRIPT'.
(Other definitions for script that I've seen before include "Written form (of play etc)" , "Written copy of words to be spoken" , "Written version of a play" , "Dialogue" , "Written version of a dramatic composition" .)