With the war lost and refusing to live under Yankee domination, Confederate soldier Tyler Grayson heads west. Taking a steamer up the Missouri River, Grayson is determined to start a new life with allegiance to no-one. However, Grayson is befriended by Jericho, a twelve year old ex-slave and cabin boy who becomes Grayson's constant companion. Aboard the steamer, Lilly Kendrick, the widow of a Yankee officer, discovers to her shame that she is attracted to Grayson. Thrown together by circumstance, Grayson, Kendrick and Jericho travel by stage across Montana Territory to the gold strike of Last Chance Gulch, now called Helena.
In Helena, Lilly's uncle is accused of murder and quickly convicted by Helena's vigilantes. Lilly is forced to ask Grayson for help and in the process confront her growing admiration for the Confederate. Unaware of Lilly's emotional dilemma and suppressing his own attraction to the young widow, Grayson agrees to help.
With only hours before sentence is carried out at the Hanging Tree, Grayson races against the setting sun to investigate the crime. Enlisting Jericho's assistance, Grayson begins to unravel a complex murder plot designed to manipulate the vigilantes and steal the gold claims of two innocent miners.