Beneath the sewer grates and manholes of the city lies a strange and secret world called the Downside. Every Downsider knows that it's forbidden to go Topside, and most fear a collision of the two worlds. But fourteen-year-old Talon is curious about what goes on above ground, and one day he ventures out. There he meets Lindsay, who is as curious about Talon's world as he is about hers. However, she also questions its origins. Then an accident threatens to crush Talon's world, and his loyalty is put to the test. Can the truth save the Downside, or will it destroy an entire civilization?