Frighten spy (5)
I believe the answer is:
spook
I believe this clue is a double definition.
'frighten' is the first definition.
(I've seen this before)
'spy' is the second definition.
(spook can informally mean a spy)
(Other definitions for spook that I've seen before include "agent" , "Enterprise propels him" , "Ghost - US spy" , "Startle - spy" , "Ghost, spectre" .)