Cartography has long been a dying art—the allure of worlds undiscovered giving way to a thoroughly charted globe captured through satellite images. Yet map-making has been the trade and obsession of Nell Young’s family for as long as she can remember. When she gets a call that her father has died, she is not surprised to find a map hidden in a secret compartment in his desk. He is the head curator of the maps department at the New York Public Library after all, but he specialized in rare artifacts, so this old gas station map is not what she expected. But as Nell sorts through the remnants of her father’s life, she comes to realize that the old gas station map in her possession is far more than it seems. All other known copies have been reported as missing or stolen, and this map is priceless. Because if the rumors are true, just beyond reach is a hidden realm—and Nell's map has thrust her into a deadly race to control this real place that should only exist on paper.