Spy (6,5)
There are a few possibilities for this:
'spy' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for secret agent that I've seen before include "Spy" , "007 - centre stage (anag)" , "Conrad character" .)
'spy' is the definition.
(double agent is a kind of spy)
This is the entire clue.
(Other definitions for double agent that I've seen before include "AA man?" , "Treacherous spy" .)
'spy' is the definition.
(secret agent)
This is all the clue.
(Other definitions for agent that I've seen before include "One does business on behalf of another" , "Author" , "envoy" , "Spy; service provider" , "Representative - means" .)
'spy' is the definition.
(spook can informally mean a spy)
This is all the clue.
(Other definitions for spook that I've seen before include "Ghost - US spy" , "agent" , "Frighten - haunt - spy" , "Enterprise propels him" , "Startle - spy" .)
'spy' is the definition.
(mole is a kind of spy)
This is the entire clue.
(Other definitions for mole that I've seen before include "Heap of soil (a 6 mountain?)" , "Counterspy" , "Spy, skin spot and furry animal" , "Pier" , "Subterranean mammal" .)
'spy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for operative that I've seen before include "secret agent" , "Significant" , "Functioning; worker" , "Having force - skilled worker" , "Machinist - working" .)