In 1803 President Thomas Jefferson selected his personal secretary, Captain Meriwether Lewis, to lead a voyage up the Missouri River to the Rockies, over the mountains, down the Columbia River to the Pacific Ocean, and back. Lewis and his partner, Captain William Clark, made the first map of the trans-Mississippi West, provided invaluable scientific data on the flora and fauna of the Louisiana Purchase territory, and established the American claim to Oregon, Washington, and Idaho.

Ambrose has pieced together previously unknown information about weather, terrain, and medical knowledge at the time to provide a vivid backdrop for the expedition. Lewis is supported by a rich variety of colorful characters, first of all Jefferson himself, whose interest in exploring and acquiring the American West went back thirty years. Next comes Clark, a rugged frontiersman whose love for Lewis matched Jefferson's. There are numerous Indian chiefs, and Sacagawea, the Indian girl who accompanied the expedition, along with the French-Indian hunter Drouillard, the great naturalists of Philadelphia, the French and Spanish fur traders of St. Louis, John Quincy Adams, and many more leading political, scientific, and military figures of the turn of the century.

High adventure, high politics, suspense, drama, and diplomacy combine with high romance and personal tragedy to make this outstanding work of scholarship as readable as a novel.