It's late summer, 1805.

A group of explorers are trekking across the Louisiana Territory, a vast expanse of wilderness

that President Thomas Jefferson recently bought from the French, thereby doubling the size

of the United States.

The expedition, known as the Corps of Discovery, is being led by two military officers from

the South.

Maryweather Lewis.

For the last time, if we want to reach the Rocky Mountains before the freeze over, I say

we take this path.

And William, Clark.

But I say if we want to reach the Rocky Mountains before they freeze over, we take this

path.

That path will just loop us back the way we came.

President Jefferson has tasked Lewis and Clark with learning everything they can about

these 828,000 square miles of Frontierland west of the Mississippi River.

He's leaving their home base of St. Louis, Missouri.

They've been keeping journals, making maps, and jotting down the plants and animals they've

found.

I'm sorry, Clark, but if we take your path, we'll never get to the Rockies before they freeze

over, and then we'll never get across.

No, I'm sorry, Lewis.

If we take your path, we'll never get to the Rockies before they freeze over, and then

...