In the early years of the century, Nathan Walker leaves the Okefenokee swamps of his native Georgia for New York City and the most dangerous job in America. A sandhog, he burrows beneath the East River, digging the underground tunnel that will carry trains between Brooklyn and Manhattan.

In the bowels of the riverbed the sandhogs - black, white, Irish, Italian - dig together; above ground, though, the men keep their distance until a spectacular accident welds a bond between Walker and his fellow sandhogs that will bless and curse the next three generations.

Years later, Treefrog, a homeless man driven below by a shameful secret, endures a punishing winter deep in his subway nest. In tones ranging from bleak to dark to disturbingly funny, Treefrog recounts his strategies of survival - killing rats, scavenging for soda cans, washing in the snow, sleeping through the cold - in New York's netherworld.

Between Nathan Walker and Treefrog stretch seventy years of ill-fated loves, unintended crimes, and social taboos. The two stories fuse to form a tale of family, race, and redemption.