Kelly's is the first book (7)
I believe the answer is:
genesis
'first book' is the definition.
(first book of the Bible)
'kelly's is' is the wordplay.
'kelly's' becomes 'gene's' (I've seen this in other clues).
'genes'+'is'='GENESIS'
'the' is the link.
(Other definitions for genesis that I've seen before include "Beginning (in the Bible)" , "Origin -- see sign (anag)" , "First book of the Bible" , "Bible's first book" , "rock group" .)