Crossword Genius

Abandoned rest, upset indeed (8)

Ross

I believe the answer is:

deserted

I'm a little stuck... Click here to teach me more about this clue!

'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" .)

I've seen this clue in The Daily Express.
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