Sacajawea a Shoshoni young woman is captured, pregnant & living among the Mandan tribe when Lewis & Clark Expedition arrives.  They are looking for a translator when the expedition winters at the reservation. When the tribal elders persuade Captain Clark, they must take pregnant Sacajawea & her scurrilous, French fur trader husband, Charbonneau, the Captains are shocked. The chiefs clarify they will need to trade with the Shoshoni for horses for there is no waterway across the Rocky Mountains.

The Mandan Chiefs reveal Sacajawea, a Shoshoni, is living among them. Lewis and Clark will need help from her, the Shoshone, to lead them over the mountains. Charbonneau drags Sacajawea to meet Lewis & Clark.