One part of play involving books is untouched (6)
I believe the answer is:
intact
'untouched' is the definition.
(I've seen this before)
'one part of play involving books' is the wordplay.
'one' becomes 'i' (Roman numeral).
'part of play' becomes 'act' (a play is made up of acts).
'involving' means one lot of letters goes inside another.
'books' becomes 'NT' (New Testament).
'i'+'act'='iact'
'iact' placed around 'nt' is 'INTACT'.
'is' acts as a link.
(Other definitions for intact that I've seen before include "Unbroken and unimpaired" , "Complete - unbroken" , "Entire, undamaged" , "Not damaged in any way" , "Entire and whole" .)