A modern novel? That is highly unlikely (5,2)
I believe the answer is:
dream on
'is highly unlikely' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'a modern novel?' is the wordplay.
'novel?' indicates anagramming the letters (I've seen 'novel' mean this (letters in a new or novel order)).
'a'+'modern'='amodern'
'amodern' anagrammed gives 'DREAM ON'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for dream on that I've seen before include "That's unlikely! (colloquial)" , "Come off it!" .)