In an 18th-century European city that’s grand but decaying, a desperate and mysterious quest occurs during the year’s “Dead Days.” The period from December 27 to 31 is different from the rest of the year, though Boy doesn’t know why. His master, Valerian the magician, is urgently searching for something to save his life—but what? and why? Boy and another orphan, Willow, are dragged all over by Valerian but kept in the dark about the backstory, which involves some kind of old pact foretelling doom. The City itself is a wonderfully gloomy character with twisting alleys, forgotten catacombs, and underground canals. Sedgwick draws a cryptic line between magic and science, making some magic recognizable to modern readers (electricity) but leaving other phenomena unexplained. Can Valerian really make people vanish? Much is left untold in this fascinatingly brooding tale, but Boy discovers in a final burst of warmth that Willow will be with him whatever his future holds. (author’s note) (Fantasy. YA)