After a shipwreck in 1809, Peter finds himself the victim of amnesia. The sea captain who finds the teenager gives him the only name he knows, while others derisively dub him Peter No-Name. Eventually, Peter finds employment in a Montreal tavern where he meets a French voyageur called Boulard who changes his life irrevocably.

Boulard works for fur trader David Thompson, soon to become one of the world's most famous explorers and mapmakers. Thompson is impressed with the teenager and enlists him in his obsessive quest to establish an overland "northwest" passage to the Pacific Ocean via the Columbia River.

With Thompson, Peter embarks on an amazing series of adventures that brings him face to face with hostile Natives and exposes him to the hardships and life-threatening challenges of formidable mountains and primeval forests as the intrepid outdoorsmen canoe, ride, and sled across a continent still largely untouched by European civilization.