"Double Indemnity" novelist (4)
I believe the answer is:
'double indemnity novelist' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cain that I've seen before include "First son" , "First murderer reported in the Bible" , "Brother of Abel" , "Slayer of Abel" , "The first known murderer" .)