" Underground Airlines is a figure of speech: it's the root of a grand, extended metaphor, "pilots" and "stewards" and "baggage handlers" and "gate agents." Connecting flights and airport security. The Airlines flies on the ground, in package trucks and unmarked vans and stolen tractor-trailers. It flies in the illicit adjustment of numbers on packing slips, in the suborning of plantation guards and the bribing of border security agents, in the small arts of persuasion: by threat or cashier's check or blow job. The Airlines is orders placed by imaginary corporations for unneeded items to be shipped to such-and-such a place at such-and-such a time. "

― Ben H. Winters , Underground Airlines