Timeless achievement shown in crime film (4,4)
I believe the answer is:
cape fear
'film' is the definition.
(I've seen this before)
'timeless achievement shown in crime' is the wordplay.
'timeless achievement' becomes 'fea' (I can't explain this - if you can you should give a lot more credence to this answer).
'shown in' is an insertion indicator.
'crime' becomes 'caper' (caper is a kind of crime).
'fea' put into 'caper' is 'CAPE FEAR'.
Can you help me to learn more?
(Other definitions for cape fear that I've seen before include "Some phobia about Batman" , "film - with 23d" , "Scorsese film" , "movie? - with 25d" .)