Interior of pub — about to be done over (5)
I believe the answer is:
inner
'interior' is the definition.
(I know that interior can be written as inner)
'pub about to be done over' is the wordplay.
'pub' becomes 'inn' (an inn is a type of pub).
'about' becomes 're' ('re' means regarding or about).
'to be done over' is a reversal indicator (flipped over).
're' reversed gives 'er'.
'inn'+'er'='INNER'
'of' acts as a link.
(Other definitions for inner that I've seen before include "Opposite of outer" , "Region around bullseye" , "Part of an archery target" , "personal" , "This part of city is at the old centre" .)