Seasonal changes in nature are among the most readily observable clues to the biological effects of climate change. “It came to me,” writes acclaimed environment reporter Lynda Mapes, “You could tell the story of climate change—and more—through a single, beloved, living thing: a tree.” Mapes chronicles her yearlong quest to understand a wizened witness to our world: a red oak, over one hundred years old, in the Harvard Forest. A tree that has seen it all, from our changing relationship with nature in our industrialized and digitized lives to the altered clockwork of nature. Mapes evokes the wonder and joy of forests, and the poetics and botany of trees, living intimately with her oak through four seasons. She dives deeply into the world of self-described “tree geeks” and becomes one herself, exploring her tree from roots to crown. She also offers a clear-eyed assessment of what the tree tells us about climate change, from the heartwood at its core to the photosynthetic cycle deep in its leaves. Mixing storytelling, tree lore, and cutting-edge science, Mapes offers a new approach to thinking about how we might live together into the far future on a planet we have changed in ways we never intended—and how trees help show us the way.