Accounts book’s right behind shelf (6)
I believe the answer is:
'accounts book's' is the definition.
(I've seen this before)
'right behind shelf' is the wordplay.
'right' becomes 'r' (common abbreviation).
'behind' means one lot of letters go next to another.
'shelf' becomes 'ledge' (synonyms).
'r' after 'ledge' is 'LEDGER'.
(Other definitions for ledger that I've seen before include "Business record book" , "Book-keeper's book" , "Account book" , "record-holder" , "Old-fashioned heavy accounts book" .)