Early one morning in New York City, Will Heller, a sixteen-year-old paranoid schizophrenic, gets on an uptown B train alone. Will is on a mission to save the world from global warming-to do it, though, he'll need to cool down his own body first. And for that he'll need one willing girl.

Lowboy tells the story of Will's odyssey through the city's tunnels, back alleys, and streets in search of Emily Wallace, his one great hope. It also follows his mother, Violet Heller, as she tries desperately to find her son before psychosis claims him completely. Violet is joined by Ali Lateef, a missing-persons specialist, who learns over the course of the day that more is at stake than the recovery of a runaway teen: Will Heller has a chilling case history, and Violet-beautiful, enigmatic, and as tormented as her son-harbors a secret that Lateef will discover at his own peril.