Soppy book about island on line (9)
I believe the answer is:
emotional
'soppy' is the definition.
(soppy can mean emotional or sentimental)
'book about island on line' is the wordplay.
'book' becomes 'tome' (a tome is a book).
'about' shows that the letters should be reversed in order.
'island on line' becomes 'ional' (I am not sure about this - if you are sure you should believe this answer much more).
'tome' reversed gives 'emot'.
'emot'+'ional'='EMOTIONAL'
(Other definitions for emotional that I've seen before include "Loving" , "Very affected; upset" , "Worked up, upset" , "Passionate" , "Impassioned - excitable" .)