Excellent detective in film (9)
I believe the answer is:
goldeneye
'film' is the definition.
(I've seen this before)
'excellent detective' is the wordplay.
'excellent' becomes 'golden' (I've seen this before).
'detective' becomes 'eye' (as in a private eye).
'golden'+'eye'='GOLDENEYE'
'in' acts as a link.
(Other definitions for goldeneye that I've seen before include "Northern diving duck - 1995 Bond film" , "spy film" .)