Plotter, conspirator (7)
I believe the answer is:
schemer
I believe this clue is a double definition.
'plotter' is the first definition.
(synonyms)
'conspirator' is the second definition.
(thesaurus)
(Other definitions for schemer that I've seen before include "Plotter and planner" , "Secret plotter" , "Person who plots" , "Plotter, conspirator" , "Machiavellian type" .)