The Sword Stonecutter is missing - stolen from Prince al-Farabi's desert caravan, from the tent of young Kasimir, a physician en route to the city of Eylau in search of employment. Fortunately, at the next oasis Kasimir encounters the legendary Magistrate Wen Chang, whose black, glittering eyes (it is said) can see into the secret hearts of men and women.

It is even greater good fortune that Wen Chang undertakes the finding of Stonecutter, for his strength is more powerful than magic: it is intelligence.

As al-Farabi follows the thief's trail into the desert, Wen Chang and Kasimir make their way toward Eylau. In the walled city, where the Red Temple, devoted to sensual pleasures, has engaged the great sculptor Robert de Borron to create new statuary, Kasimir encounters embarrassment and Natalia, a young woman who is more beautiful unclothed than clothed.

Meanwhile, Wen Chang has learned of a certain fabulous diamond, and of Mistress Headmark, the lapidarist whose duty it will be to cleave it, perfectly. Either a lapidarist or a sculptor would have great use for Stonecutter. . . but so would the smoothest assassin Eylau has ever seen.