U.S. Senator William Tadlock (Kirk Douglas) is leaving his home in Missouri in 1843, heading west on the Oregon Trail by wagon train. His son and slave come along, with Dick Summers (Robert Mitchum) as a hired guide. Joining them on the expedition are farmer Lije Evans (Richard Widmark), his wife Rebecca (Lola Albright), and 16-year-old son Brownie (Michael McGreevey). Among others there are also the newlyweds Johnnie (Michael Witney) and Amanda Mack (Katherine Justice), plus the Fairman and McBee families.