Index in a story book (5)
I believe the answer is:
table
'index' is the definition.
(I've seen this before)
'in a story book' is the wordplay.
'in' is an insertion indicator.
'a story' becomes 'tale' ('tale' can be a synonym of 'story').
'book' becomes 'b' (abbreviation for book).
'tale' going around 'b' is 'TABLE'.
(Other definitions for table that I've seen before include "Put forward for formal discussion" , "Food - list" , "Board < put on" , "Flat-topped piece of furniture" , "Record" .)