Caught holding up a claims office to pay off a gambling debt, gunman Tom Horn (Barry Sullivan) is tossed in a cell with William Morgan (Broderick Crawford), the leader of an outlaw gang. Busted out by his men, Morgan invites Horn to join them and soon makes the loner his second-in-command. Killing anyone who gets in their way, the outlaws steal a fortune in gold before hiding out in Tombstone, a lawless frontier town. When Horn's new bride (Marjorie Reynolds) urges him to take his cut and quit Morgan and the gang, it leads to double-crosses and murder as the two desperados plot to kill each other rather than split up all the loot.