plotter (n.)

• betrayer
• cockatrice
• coconspirator
• conspirator
• double-crosser
• double-dealer
• exploiter
• finagler
• informer
• intriguer
• machinator
• maneuverer
• operator
• opportunist
• quisling
• rat
• schemer
• serpent
• snake
• timeserver
• traitor
• treasonist
• trimmer
• turncoat
• wire-puller