Power group scheme (4)
I believe the answer is:
plot
'scheme' is the definition.
(plot is a kind of scheme)
'power group' is the wordplay.
'power' becomes 'p'.
'group' becomes 'lot' (lot is a kind of group**).
'p'+'lot'='PLOT'
(Other definitions for plot that I've seen before include "See 12 Across" , "lost in poor judgment" , "... of story, family ..." , "garden area" , "Conspire - small piece of land" .)