Complete one part of play about books (6)
I believe the answer is:
intact
'complete' is the definition.
(intact can mean complete or undamaged)
'one part of play about books' is the wordplay.
'one' becomes 'i' (Roman numeral).
'part of play' becomes 'act' (a play is made up of acts).
'about' is a charade indicator (letters next to each other).
'books' becomes 'NT' (New Testament).
'act' put after 'nt' is 'ntact'.
'i'+'ntact'='INTACT'
(Other definitions for intact that I've seen before include "Whole and unharmed" , "Inviolate" , "Complete - undamaged" , "Not damaged in any way" , "Undamaged, not broken" .)