Greene's novel keeping one's fire up (8)
I believe the answer is:
energise
'fire up' is the definition.
(fire up can mean to energise or stimulate)
'greene's novel keeping one's' is the wordplay.
'novel' indicates an anagram (letters in a new or novel order).
'keeping' indicates putting letters inside.
'one's' becomes 'I's' (Roman numeral).
'greene' anagrammed gives 'energe'.
'energe' placed around 'is' is 'ENERGISE'.
(Other definitions for energise that I've seen before include "Give power to" , "Stimulate activity" , "give vigour" , "Give active force" , "Motivate" .)