Farmer digesting extremes of horror in crime novel (8)
I believe the answer is:
thriller
'crime novel' is the definition.
'farmer digesting extremes of horror' is the wordplay.
'farmer' becomes 'tiller' (I've seen this before).
'digesting' is an insertion indicator (inserted letters are eaten or ingested).
'extremes of' suggests removing the centre (only the letters at the extremes of the word).
'horror' with its centre taken out is 'hr'.
'tiller' placed around 'hr' is 'THRILLER'.
'in' acts as a link.
(Other definitions for thriller that I've seen before include "exciting event" , "The Birds', say" , "suspenseful book?" , "best-selling album" , "Let her trill in exciting book or film" .)