Real-life spy Richard Sorge and scenes of pre-WW II China are among the touches that make plausible this rather romantic treatment of the continuing search for a ""fifth man,"" the last of the master spies for the Soviets still hiding as moles in British Intelligence. This time the search involves Ruth Kuczynsky, who, as a young wife in Shanghai in the 1930's, became a passionate and lifelong communist and spy for the Soviets. Recruited by Richard Sorge, who also became her lover, Ruth was sent back to Europe and then England, where she was involved in the theft of nuclear technology. During her stay she was protected by ""Alec,"" a traitor in the innermost circle of the intelligence establishment. Forty years later, after Ruth returns to East Germany, Alec's identity is still a secret, his existence never actually having been proven, but the request for asylum by an East German scientist claiming to be Ruth's son seems at last to offer the key to Alec's identity. The British offer asylum only if he can escape with his mother and her secrets. Current events in the U.K. lend credence to this unfashionably but mercifully intelligible thriller. By the author of Down Among the Dead Men (1983) and Seven Steps to Reason (1984).