It is unlikely, all things considered, that you have heard of the Treaty of Detroit. Unliklier still that you have heard of it by its other name: the Treaty of the Underpeople. Since that day when the secret war, started in those salt mines, had ended in an uneasy peace, our industry and excess have had their unseen mirror underfoot. Our permissions, implicitly given, for every floor of every building stacked toward the sky to have its own subterranean reflection burrowed into the earth. The Underpeople thrive below, the roots and foundations of their civilization inextricably entwined with our own.