While in college, Edith Widder's childhood dream of becoming a marine biologist was almost derailed when complications from a surgery caused temporary blindness. Upon her recovery, she became fascinated with oceanic bioluminescence, and trained as a submersible pilot. In this richly layered memoir, Widder evokes the darkness of the deep—which is lit by mysterious organic lights—and describes the unique ecosystem that is home to microbes, the giant squid, and otherworldly comb jellies.