Point to agent in sight (4)
I believe the answer is:
espy
'sight' is the definition.
(espying is a kind of sighting)
'point to agent' is the wordplay.
'point' becomes 'e' (E is an example).
'to agent' becomes 'spy' (spy is a kind of agent).
'e'+'spy'='ESPY'
'in' acts as a link.
(Other definitions for espy that I've seen before include "Spot at a distance" , "Perceive" , "Detect" , "Pick out at a distance" , "See" .)