Masterminds in Greene's novel (9)
I believe the answer is:
engineers
'masterminds' is the definition.
('engineer' can be a synonym of 'mastermind')
'in greene's novel' is the wordplay.
'novel' indicates an anagram.
'in'+'greenes'='ingreenes'
'ingreenes' anagrammed gives 'ENGINEERS'.
(Other definitions for engineers that I've seen before include "They design roads, bridges etc." , "professionals?" , "They solve practical problems using scientific knowledge" , "Masterminds" , "Contrives" .)