Abandoned rest, upset indeed (8)
I believe the answer is:
deserted
'abandoned' is the definition.
(synonyms)
'rest upset indeed' is the wordplay.
I cannot really understand how this works, but
an anagram of 'rest' is 'sert' which is located in the answer.
The remaining letters 'deed' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for deserted that I've seen before include "Abandoned, forsook" , "Illegally left army" , "defected,renounced" , "Uninhabited" , "Ran away from army" .)