More than a year and many hundreds of miles into their expedition, Lewis and Clark face their biggest hurdle yet: unless they acquire horses to carry them over the mountains, they will fail in their mission to reach the Pacific Ocean. With hope all but gone, Sacagawea, their young Shoshone interpreter, guides them to her tribal village. Though she knows it will forever change her people's way of life, Sacagawea helps obtain the horses, and thus ensures the completion of the historic journey.

Marilyn Weymouth Seguin is the author of eight historical books for young readers. Marilyn teaches in the English Department at Kent State University.