Drug dealer in revolutionary film (7)
I believe the answer is:
chemist
'drug dealer' is the definition.
(I've seen this before)
'revolutionary film' is the wordplay.
'revolutionary' becomes 'Che' (Che Guevara the Marxist revolutionary).
'film' becomes 'mist' (to film over is to mist or fog over).
'che'+'mist'='CHEMIST'
'in' is the link.
(Other definitions for chemist that I've seen before include "Faraday, for example" , "Dispenser of prescribed medicines" , "drugs supplied by me?" , "Pharmacist, say" , "Drug seller" .)