Is sure upset at having done wrong! (4)
I believe the answer is:
rues
'having done wrong' is the definition.
I can't tell whether this defines the answer.
'is sure upset' is the wordplay.
'upset' indicates an anagram.
'sure' with letters rearranged gives 'RUES'.
'at' acts as a link.
Can you help me to learn more?
(Other definitions for rues that I've seen before include "Bemoans" , "Is sorry for - plants" , "Regrets, to be sure" .)