Mole or plant (3)
I believe the answer is:
spy
I believe this clue is a double definition.
'mole' is the first definition.
(I've seen this before)
'plant' is the second definition.
(a plant can be a person positioned to act as a spy)
(Other definitions for spy that I've seen before include "Enemy agent" , "Glimpse" , "Spot" , "Catch sight of" , "One gathers information on enemies" .)