With the trapping trade on the decline, mountain man Barnaby Skye takes work as a guide, leading a wealthy Englishman, Graves Duplessis Mercer, and two companions on an exploration of the Yellowstone and Missouri River valleys. Mercer is a peculiar employer. He has come to the American wilderness seeking weird, morbid, thrilling, preferably slightly salacious, material to write up for British tabloids. He has little interest in such amazing natural phenomena as the geysers of the Yellowstone country but is adept in ferreting out stories of cannibalism and similar atrocities. To the Briton's disappointment, Skye has none of these to offer but does agree to take him to a Missouri River valley where gigantic bones of ancient monsters thrust out of canyon walls. Skye's Crow Indian wife, Victoria, warns that the bones are sacred among certain tribes, but Mercer insists on taking a "trophy" - a tooth from a tyrannosaurus-like fossil. This act nearly costs the lives of Mercer's party and its guide, Barnaby Skye.