Most biographies start with their subject’s ancestry, but Laura Dassow Walls introduces Henry David Thoreau (Chicago, $35) by way of a survey of New England’s geography. She explains the region’s kettle ponds, drumlins, and rocky promontories, and describes the ways of its indigenous peoples. These were Thoreau’s early fascinations, and they shaped his entire life. As she traces how his ideas about nature, social justice, and transcendentalism grew from and supported each other, Walls brilliantly puts Thoreau’s thinking about ecology, equality, and a “higher law” into the context of his time and shows how very much ahead of his time he was—to the point that editors censored his essays. Much of her remarkable portrait revises common assumptions about Thoreau. He was neither a recluse nor a misanthrope. He joined many groups, lectured frequently, and made lifelong, devoted friends, including Emerson and Horace Greeley, who acted as his literary agent. Living “deliberately” at Walden Pond did not mean living alone. Thoreau had constant visitors there and became part of an overlooked community of freed slaves, Irish immigrants, and the impoverished. He aligned himself with the marginalized ever after. Walls has done prodigious research for this deeply affecting book. She explains why good pencils were so hard to make in the nineteenth century, shows us step-by-step how Thoreau built his Walden house, takes us on his hiking and boating trips, and traces his evolving ideas. The result is a Thoreau you don’t just know more about, but a living, breathing, thinking person you feel you really know.