Book promoted by the setter's controversial (7)
I believe the answer is:
emotive
'controversial' is the definition.
(I've seen this before)
'book promoted by' is the wordplay.
'book' becomes 'tome' (tome is a kind of book).
'promoted' shows that the letters should be reversed in order (going up, in a down clue).
'by' becomes 'ive' (I can't explain this - if you can you should believe this answer much more).
'tome' written backwards gives 'emot'.
'emot'+'ive'='EMOTIVE'
'the setter's' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for emotive that I've seen before include "Generating feelings" , "Argumentative" , "Stirring feeling" , "Causing strong feelings" , "Highly-charged" .)