The Ambushers
Donald Hamilton
 Matt Helm conducts a by-the-book assassination in the (fictional) Central American nation of Costa Verde. Afterwards, he finds himself pursuing an ex-Nazi named von Sachs, who has obtained one of the nuclear missiles that had been bound for Cuba during the Cuban Missile Crisis, and who is threatening the United States with the weapon. Along the way he finds himself working with a Russian agent named Vadya (who would return in later Helm adventures).