Control party underling (8)
I believe the answer is:
dominion
'control' is the definition.
(I've seen this before)
'party underling' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'underling' becomes 'minion' (I've seen this before).
'do'+'minion'='DOMINION'
(Other definitions for dominion that I've seen before include "Area of control" , "Government" , "Realm" , "eg Canada" , "power" .)