Crooked aristocrat caught — one beyond redemption (5-3)
I believe the answer is:
write-off
'one beyond redemption' is the definition.
(person or thing which cannot be saved or repaired)
I can't explain the remainder of the clue.
(Other definitions for write-off that I've seen before include "Cancel, a debt perhaps" , "To destroy irredeemably" , "Send a letter - cancel a debt" , "Vehicle too badly damaged to repair" , "Give up on, recognise as lost like bad debt" .)