Cox swam the English Channel at fifteen, and was the first to swim off Antarctica in 32-degree water without a wetsuit. But this story starts at a laboratory at the University of London, with Cox hooked up to thermocouples and probes, with three scientists trying to make sense of her extraordinary human capabilities. The test results paved the way for new medical and life-saving practices. When Cox was later diagnosed with atrial fibrillation (AFib), she was in fear of living out a lesser life as an invalid. Here, Cox writes of her full surrender to her increasing physical frailty, to her illness, her treatment, her slow pull toward recovery.