Plot to put fifty in the pot (4)
I believe the answer is:
plan
'plot' is the definition.
(plot can mean to conspire or plan)
'fifty in the pot' is the wordplay.
'fifty' becomes 'L' (Roman numeral).
'in the' means one lot of letters goes inside another.
'pot' becomes 'pan' (I've seen this before).
'l' put inside 'pan' is 'PLAN'.
'to put' acts as a link.
(Other definitions for plan that I've seen before include "chart" , "Intend" , "Diagram; design" , "Programme" , "Scale drawing; scheme" .)