On a bitter winter's day in 1916, deep below the streets of New York, a group of men are working in one of the huge pressurised tunnels that will make up the subway system. Suddenly, a tiny hole appears in the roof of the tunnel and air rushes in, sucking the men up through the bed of the Hudson, to be suspended on a plume of water high above the river. Almost ninety years later, a homeless man stumbles on the same corridor and sets about making his home deep under the city.