In the mid-19th century, Senator William J. Tadlock leads a group of settlers overland in a quest to start a new settlement in the Western US. Tadlock is a highly principled and demanding taskmaster who is as hard on himself as he is on those who have joined his wagon train. He clashes with one of the new settlers, Lije Evans, who doesn't quite appreciate Tadlock's ways. Along the way, the families must face death and heartbreak and a sampling of frontier justice when one of them accidentally kills a young Indian boy.

Doc Holliday travels to Tombstone, Ariz., with prostitute Katie Elder. Although the trip is difficult because Doc is ill with tuberculosis, they eventually reach their destination, where Holliday is reunited with his old friend Marshal Wyatt Earp, who has been clashing with the Clanton gang. Tensions between Earp and the Clantons rise until their infamous final showdown brings it to a head.