Part of book taken out in theatre! (8)
I believe the answer is:
appendix
'part of book' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
(Other definitions for appendix that I've seen before include "Subsidiary section" , "extra pages" , "Supplement at the end of a book" , "It contains supplementary material" , "part of book" .)