Rest that one, in all fairness, deserves? (3,5,2,3,4)

'all fairness deserves?' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'rest that one' is the wordplay.
I cannot really understand how this works, but
'rest' could be 'sleep' (synonyms) and 'sleep' is found in the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

'in' is the link.

Can you help me to learn more?