Fourteen-year-old Francis Tucket is heading west on the Oregon Trail with his family by wagon train. When he receives a rifle for his birthday, he is thrilled that he is being treated like an adult. But Francis lags behind to practice shooting and is captured by Pawnees. It will take wild horses, hostile tribes, and a mysterious one-armed mountain man named Mr. Grimes to help Francis become the man who will be called Mr. Tucket.

Francis Tucket, Lottie and Billy have survived extraordinary, hair-raising adventures in their quest to find Francis's family, lost when he was kidnapped from a wagon train on the Oregon Trail. Now they meet up with a British explorer, bloodthirsty soldiers, and in a tragic, heroic encounter, with Jason Grimes, the mountain man. Their way is made more treacherous still by the secret they carry, the ancient gold they discovered in a Spanish grave. In this final adventure they head home at last, and an epilogue tells what happens to them on the Oregon frontier.