Mr. Kelly's is the first book (7)
I believe the answer is:
genesis
'first book' is the definition.
(first book of the Bible)
'mr kelly's is' is the wordplay.
'mr kelly' becomes 'genes' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'genes'+'is'='GENESIS'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for genesis that I've seen before include "rock band" , "name of group" , "Origin; Bible book" , "First book of the Bible" , "religious book?" .)