Ace, then service returned at a distance (4)
I believe the answer is:
afar
'at a distance' is the definition.
(I've seen this before)
'ace then service returned' is the wordplay.
'ace' becomes 'a' (abbreviation).
'then' is a charade indicator (letters next to each other).
'service' becomes 'raf' (Royal Air Force).
'returned' shows that the letters should be reversed in order.
'raf' in reverse letter order is 'far'.
'a'+'far'='AFAR'
(Other definitions for afar that I've seen before include "A long way away" , "At a distance (poetic)" , "Many miles away" , "quite some distance" , "A long distance away" .)