The story begins in 1911, where former outlaw John Marston is taken from his family by Bureau of Investigation agents Edgar Ross and his partner, Archer Fordham, and will only be granted amnesty when he brings the remaining members of his old gang to justice. John is escorted to the town of Armadillo and sets off to track down former ally Bill Williamson. He confronts Williamson and his men at their stronghold, Fort Mercer, only to be shot and left for dead. Local rancher Bonnie MacFarlane finds him critically wounded and takes him to her ranch for recovery. Several days later, John begins performing tasks and favors for various allies in exchange for their help with organizing an attack on Fort Mercer. John and his group then breach the fort and defeat Williamson's gang only to find that Williamson has fled to Mexico to seek help from Javier Escuella, another former member of John's gang.
