Police officer in Cape, working with firm (9)
I believe the answer is:
constable
'police officer' is the definition.
'cape working with firm' is the wordplay.
'cape' becomes 'c' (abbreviation used on maps).
'working' becomes 'on'.
'with' is a charade indicator (letters next to each other).
'firm' becomes 'stable' ('stable' can be similar in meaning to 'firm').
'c'+'on'+'stable'='CONSTABLE'
'in' is the link.
(Other definitions for constable that I've seen before include "Bobby" , "Law enforcer" , "In England, a great painter or lowly policeman" , "Copper - artist" , "Force member" .)