Was plain-clothes police supremo bad? (6)
I believe the answer is:
rancid
'bad?' is the definition.
(I've seen this before)
'was plain-clothes police supremo' is the wordplay.
I cannot really understand how this works, but
'police' could be 'cid' (abbreviation for Criminal Investigation Department) and 'cid' is found within the answer.
The remaining letters 'ran' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rancid that I've seen before include "Smelly and going bad" , "Turned -- malodorous" , "Sour - smelling bad" , "(Of fatty foods) stale" , "Smelling or tasting bad" .)