These historical mysteries, featuring a Tang-era Chinese magistrate, follow the tradition of ancient Chinese suspense novels. Apart from the pleasure of the elaborate plots, the books are rich in details of court and daily life in ancient China. In this book set on the northern frontier of Pei-chow, Judge Dee must solve the murders of an honored merchant, a kindly boxing master, and a paper merchant's wife, whose corpse has no head. The nail murder is based on a 13th-century tale. This is the fourth installment of Robert Van Gulik's classic Chinese mystery series.  (CHN292, $12.95)