Mysterious copper squashed between two officers (6)
I believe the answer is:
occult
This clue might be a double definition.
'mysterious' is the first definition.
(I've seen this before)
'copper squashed between two officers' is the second definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
Can you help me to learn more?
(Other definitions for occult that I've seen before include "Involving supernatural phenomena" , "Hidden - paranormal" , "Supernatural forces and events and beings" , "Mystical (black arts)" , "Secret - mysterious" .)