Plan to shoot about fifty (4)
I believe the answer is:
plot
'plan' is the definition.
(I know that plot is a type of scheme)
'shoot about fifty' is the wordplay.
'shoot' becomes 'pot' (I've seen this in other clues).
'about' is an insertion indicator.
'fifty' becomes 'l' (Roman numeral).
'pot' placed around 'l' is 'PLOT'.
'to' acts as a link.
(Other definitions for plot that I've seen before include "Small area of ground" , "Conspiracy, secret plan" , "Vegetable garden - scheme" , "Scheme or small piece of land" , "Secret plan; graph" .)