Is traitor returning bones? (5)
I believe the answer is:
tarsi
'bones?' is the definition.
(I've seen this before)
'is traitor returning' is the wordplay.
'traitor' becomes 'rat' (I've seen this before).
'returning' is a reversal indicator.
'is'+'rat'='israt'
'israt' backwards is 'TARSI'.
(Other definitions for tarsi that I've seen before include "parts of leg" , "collections of bones?" , "Bones of the ankles and heels" , "Foot bones" , "Ankle bones" .)