Factory spy (5)
I believe the answer is:
plant
I believe this clue is a double definition.
'factory' is the first definition.
(I've seen this before)
'spy' is the second definition.
(someone planted somewhere to spy)
(Other definitions for plant that I've seen before include "Spy; manufacturer's site" , "Living organism without locomotion" , "sold by garden centre" , "Hide in order to be found" , "Shrub - factory" .)