Windmills of the Gods by Sidney Sheldon

She's on the glinting edge of East_West confrontation, a beautiful and accomplished scholar who has suddenly become our newest ambassador to an Iron Curtain country, a woman who is about to dramatically change the course of world events-if she lives.
For Mary Ashley has been marked for death by the world's most proficient and mysterious assassin, and plunged into a nightmare of espionage,kidnapping, and terror. Here, only two people-both powerfully attractive and ultimately enigmatic men-can offer her help. And one of them wants to kill her.