The Mandarin Cypher — Adam Hall

Quiller is in Hong Kong, where he thinks he''s on vacation. But every alleyway leads dead to danger, and Quiller gets the message: He''s never off duty. The plot moves into a high gear. Quiller always enjoyed his rides, but this one is taxing. He finds a woman as faithless as she is beautiful; he fails to reform her, but enjoys the effort. He takes on villains one, two, and three at a time and dispatches them on land with karate and in the South Seas with its aquatic equivalent.