Spy No 2 in Slovakia (5)
I believe the answer is:
spook
'spy' is the definition.
(spook can informally mean a spy)
'no 2 in slovakia' is the wordplay.
'no 2' becomes 'poo' (number two can informally mean faeces).
'in' means one lot of letters goes inside another.
'slovakia' becomes 'SK' (abbreviation for Slovakia).
'poo' going into 'sk' is 'SPOOK'.
(Other definitions for spook that I've seen before include "Startle - spy" , "agent" , "Frighten - haunt - spy" , "Enterprise propels him" , "Ghost, spectre" .)