Once a century, for only six days, the bay around a small Washington island glows like a water-bound aurora. Dr. Rachel Bell, a scientist studying the 100-Year Miracle and the tiny sea creatures that create it, knows a secret about the phenomenon that inspired the region’s myths and folklore: the rare green water may contain a power that could save Rachel's own life. But the Miracle does things to people. Strange and mysterious things. And as these things begin to happen, Rachel has only six days to uncover and control the Miracle's secrets before the waters go dark for another hundred years.