Discover an Eastern secret agent (4)
I believe the answer is:
espy
'discover' is the definition.
(I've seen this in another clue)
'an eastern secret agent' is the wordplay.
'an eastern' becomes 'e'.
'secret agent' becomes 'spy' (spy is a kind of secret agent).
'e'+'spy'='ESPY'
(Other definitions for espy that I've seen before include "Behold" , "Perceive" , "Observe, notice" , "Catch sight of (poetic)" , "Pick out at a distance" .)