On June 13, 1805, Meriwether Lewis crested a rise and heard the Great Falls of the Missouri — cascades dropping nearly ninety feet. He wrote that it was "the grandest sight I ever beheld," then spent four weeks portaging eighteen miles around it through cactus and heat that exceeded 100 degrees. Awe and ordeal, inseparable: that is the texture of the Lewis and Clark history.

Into the Unknown is the complete story of the Corps of Discovery: eight thousand miles, two and a half years from Camp Dubois to the Pacific and back. Walter Franklin Osgood traces every stage — from Jefferson's Louisiana Purchase and his 1803 scientific instructions to Lewis, through the Bad River standoff, the winter at Fort Mandan where Sacagawea joined the Corps, her reunion on the continental divide when she recognized Shoshone chief Cameahwait as her own brother, the eleven-day Bitterroot ordeal, and the return to St. Louis in September 1806.

Inside this American exploration book:

• Jefferson's Louisiana Purchase — a $15 million purchase that doubled the republic overnight and made the Corps of Discovery a matter of national sovereignty (Chapter 1)
• The Bad River confrontation — Clark's drawn sword, the aimed swivel gun, and the Partisan's grabbed bowline: the most dangerous diplomatic moment of the expedition (Chapter 6)
• Sacagawea — she saved the navigational instruments from a capsizing pirogue, overheard Cameahwait's plan to abandon the Corps, and wept when she recognized the Shoshone chief as her own brother (Chapters 8, 10)
• The Great Falls portage — eighteen miles, four weeks, prickly pear through their moccasins, a failed iron boat, and Sacagawea's near-fatal illness (Chapter 9)
• Crossing the Bitterroots — eleven days, snow covering the trail, hunters returning with nothing, and the decision Clark recorded as the most critical moment of the journey (Chapter 11)
• The honest reckoning — diplomatic promises never kept, the 1837 smallpox epidemic that reduced the Mandan from 1,600 to fewer than 150, and the full consequences for the peoples the expedition encountered (Chapters 20, 24)

The Corps returned with 178 new plant species, 122 new animal species, and Clark's maps that guided American geography for decades. This narrative American history of the Lewis and Clark expedition holds both the achievement and the reckoning: the blank map filled in, and the full human cost of what filling it in meant for the peoples already living there.

For readers of Stephen Ambrose's UNDAUNTED COURAGE and S.C. Gwynne's EMPIRE OF THE SUMMER MOON.