The Tamarind Seed

Judith, a widow, starts an affair with a married RAF group captain, Richard Paterson, while working in London. When she discovers he's not leaving his wife, she takes a vacation in Barbados to nurse her emotional wounds. There, she meets a Soviet military attaché, Feodor Sverdlov, who pursues her romantically despite being married. The situation raises concerns for the British and Soviet intelligence agencies, who suspect Judith could be a double agent due to her access to valuable information and her potential to rekindle her relationship with Paterson.