Set in the Old West territory of New Mexico, 'Appaloosa' revolves around city marshal Virgil Cole (Harris) and his deputy partner Everett Hitch (Mortensen), who have made their reputation as peacekeepers in the lawless towns sprining up in the untamed land.

In the small mining community of Appaloosa, a ruthless, powerful rancher named Randall Bragg (Irons) has allowed his band of outlaws to run roughshod over town. After the cold blooded murder of Appaloosa's city marshal, Cole and Hitch are hired to bring the murderer to justice.

While establishing new authority with equal parts grit and guns, Cole and Hitch meet provocative newcomer Allison French (Zellweger), whose unconventional ways threaten to undermine their progress and to destroy the two lawmen's decade old partnership.