Ally involved in machinations (5)
I believe the answer is:
china
'ally' is the definition.
(china plate can mean a mate or friend)
'involved in machinations' is the wordplay.
'involved in' says the answer is hidden in the clue.
'CHINA' is hidden in the letters of 'machinations'.
(Other definitions for china that I've seen before include "Delicate porcelain from Cathay?" , "Tableware; country" , "Ceramic; mate" , "Ceramics; friend" , "It used to be called Cathay" .)