Award-winning writer Mary Ellen Hannibal has long reported on scientists’ efforts to protect vanishing species, but it was only through citizen science that she found she could take action herself. As she wades into tide pools, spots hawks, and scours mountains, she discovers the power of the heroic volunteers who are helping scientists measure—and even slow—today’s unprecedented mass extinction. Citizen science may be the future of large-scale field research—and our planet’s last, best hope.