Charlie's Shell Game
Written by
Brian Garfield
Copyright 1978
Gregorius was the KGB man who was in Caracas to take someone out. Charlie Dark was the CIA man sent to stop him. Dark is certain, though, that Gregorius is really planning on going after Dark so it becomes an interesting race of who stops whom first.
Originally in EQMM, Feb 1978. It is the 2nd story in the collection .