Archibald, Jockabeb, and their little sister, Tess, head off for a long weekend with their Aunt Claire in New York City, where they set about visiting the local tourist sites. Things take a disastrous turn after the boys become separated from Aunt Claire and Tess and cross paths again with the evil Tommy Nat, who almost succeeded in taking their lives in Haiti several months before. The boys frantic attempt to evade capture takes them to parts of Manhattan never listed on any tourist map, and leads them to a mysterious young girl named Willow, who knows the secrets of the city, both above and below ground."