Author Blyton? Not one to finish (3)
I believe the answer is:
end
'finish' is the definition.
(I know that finish can be written as end)
'author blyton? not one' is the wordplay.
'author blyton?' becomes 'Enid' (children's author Enid Blyton, 1897-1968).
'not' is a deletion indicator.
'one' becomes 'I' (Roman numeral).
'enid' with 'i' taken out is 'END'.
'to' acts as a link.
(Other definitions for end that I've seen before include "Purpose of finish" , "Purpose, objective" , "Finished" , "Novel by Graham Greene" , "Final part" .)