Treasure about to be returned to safe (5)
I believe the answer is:
peter
'safe' is the definition.
(I've seen this in other clues)
'treasure about to be returned' is the wordplay.
'treasure' becomes 'pet' (both are terms of endearment).
'about' becomes 're' (regarding**).
'to be returned' shows that the letters should be reversed in order (I've seen 'is returned' mean this).
're' in reverse letter order is 'er'.
'pet'+'er'='PETER'
'to' acts as a link.
(Other definitions for peter that I've seen before include "Play high card before low" , "One of the Apostles" , "Apostle - saint - first Pope?" , "Man's name" , "- Grimes (Britten)" .)