Books back in totally tropical paradise (5)
I believe the answer is:
atoll
'tropical paradise' is the definition.
(I've seen this before)
'books back in totally' is the wordplay.
'books' becomes 'OT' (Old Testament).
'back' says the letters should be written backwards.
'in' means one lot of letters goes inside another.
'totally' becomes 'all' (I've seen this in another clue).
'ot' in reverse letter order is 'to'.
'to' put within 'all' is 'ATOLL'.
(Other definitions for atoll that I've seen before include "String of islands" , "Circular coral reef" , "Pacific coral island" , "Ring-shaped coral reef enclosing a lagoon" , "Bikini, say" .)