Thirty-two days underground. No heat. No sunlight. June 4th, 1938. Nathaniel Kleitman makes his way down the seventy-one steps which lead to the mouth of Mammoth Cave. Despite the midsummer heat, he and his research student carry heavy overcoats, galoshes and several pairs of woollen trousers. They are about to embark on one of the most intrepid and bizarre experiments in medical history, one which will change our understanding of sleep forever. Pausing for a moment, Kleitman inhales, taking in the scent of the trees and the dry earth; a smell he will have near forgotten by the time he emerges from the cave a month later.

Then, together, they enter the darkness. When Kleitman arrived in New York, a penniless, twenty-year-old refugee, few would have guessed that in just a few decades he would revolutionise the field of sleep science. In Mapping the Darkness, award-winning writer Kenneth Miller weaves science and history to tell the story of the outsider scientists who took sleep science from the fringes to a mainstream obsession. Reliving the spectacular experiments, technological innovation and single-minded commitment of these early pioneers, Miller provides a tantalising glimpse into the most mysterious third of our lives.