Cape (The Cambridge Theorem, 1990) again proves that the Cold War thriller has legs by showing the inner workings of a fresh locale, the British Mission to the UN in New York--and piling on the plot twists till the mind boggles. Perhaps it should be called the Coolish War, since the story is set in an imagined post-Gorbachev period when the Yanks and their allies are negotiating with the Soviet Union over a demilitarized zone across Europe. But some unreconstructed Commies will never learn. Derek Smailes, the hero of Cape's first thriller as a Cambridge detective sergeant, is now a junior security man at the Mission, living in Brooklyn and romancing a comely Brit several social cuts above him, whom he sees as a designer socialist who would faint at a glimpse of polyester. The author makes much of New York and its ways seen through the eyes of an Englishman who was half in love with America before he crossed the pond. Cape also seems to know spycraft and the activities of the Mission from the inside, providing the sort of details that lesser writers neglect. The description of how a Russian is encouraged to defect, and then used, is of sustained interest. In general, however, Cape's Russians come across as strictly stock characters in their clichÇd milieu. But the games they play are what counts in this genre, and their wiles keep the hero jumping. There is still a touch of the methodical policeman in Smailes's makeup, which adds to his believability but may make him a little sobersided for readers who like dash in their heroes. An excellent spy yarn--with a modestly engaging British hero snarled in a complex plot.