Spot the spy (4)
I believe the answer is:
mole
I believe this clue is a double definition.
'spot' is the first definition.
(spot or blemish on the skin)
'the spy' is the second definition.
(mole is a kind of spy)
(Other definitions for mole that I've seen before include "Adrian ---, fancies Pandora; lurking spy" , "Pier" , "Small burrowing animal" , "Amount of substance" , "Spy - one that burrows" .)