Sean is an Immortal from Scotland who came to America with his mother at the time of the American Revolution. Sean eagerly joined the American's cause. In 1776, the British Army was advancing, and Sean's mother didn't want Sean to fight in the battle, but Sean wanted to fight. Sean and the rest of the Colonials engaged in battle with the British, and it was there when Sean's life was about to change.
Liam Riley, an Immortal and one of the British soldiers shot Sean and Liam realized he had just given a latent Immortal his first death. Liam told the dying man that he will live, startled by a scream, Liam shot Sean's mother. Appalled that he had just shot a woman, Liam assured her that Sean would be fine, that he would live and live a long time. Comforted, she told Liam she forgave him and then passed out.
Liam took Sean's mother to the camp hospital and Amanda, who is a camp healer, does successfully remove the bullet, but could not save her from a subsequent infection. Sean was brought to his mother by Amanda, and he was with when she died. Amanda had told the penitent and prayerful Liam only that she had successfully removed the bullet, not that the woman was dying from an infection and for the next 200 years believed his prayers had been answered and that she had lived.
In 1999, Sean was after Liam. Sean ran into Amanda and they dueled, but while fighting, a reporter, Lizzie Tynan, spotted the fight and took pictures, distracting the combatants. Sean managed to run Amanda through, but when the reporter screamed, Sean ran away.
Nick Wolfe tracked down Sean, and tried to convince him not to go after Liam, but Sean was intent on his revenge. Sean tracked Liam to his church but the priest refused to fight him. Nick and Amanda tried to stop Sean from executing Liam, but Liam tells them not to.
Liam, told Sean that he forgave him. Sean, angry asked by what right he forgave Sean. Liam answered he could because Sean's mother had forgiven him. Sean, about to take Liam's head, found he could not after all, and left Liam to ride off with his associates.