11-year-old Reuben Pedley lives with his mother in the Lower Downs--gloomy New Umbra's gloomiest and most run-down neighborhood. Men called Directions patrol the streets, and everyone lives in fear of getting on The Smoke's bad side. Everyone knows that The Smoke really runs New Umbra, even if no one has ever seen him. Is he a ghost? A phantom?

Reuben is shy and friendless. During the day, he sneaks around the streets of the Lower Downs, searching for hiding places and climbing to impossible perches. One day, Reuben finds something odd on one of his escapades. High up on the side of a building, a spherical clock watch is hidden in a wooden box. Reuben soon learns that his discovery has yielded more than a sellable antique; the watch turns its holder invisible. While this discovery is exhilarating, possession of the watch comes with several prices; not only is the holder blind to his surroundings while invisible, and extremely tired once the invisibility has passed, but the possessor of the watch is in grave danger. The Smoke, it seems, has been searching for this very same watch for a very long time. And he will stop at nothing to obtain it.

Finding himself and his mother in danger, Reuben searches for more information on his discovery. His search brings him to the clock-repair shop of Mrs. Genevieve, an old woman who seems more concerned for Reuben's safety than Reuben is himself. Finally, Reuben finds himself at the lighthouse of a certain Meyer family; a clan of steadfast redheads dedicated to lighthouse-keeping since the founding of Point William. Reuben, little Penny Meyer, and her brother Jack unravel the great mystery of the watch--and the dangerous mission its possession entails.