A little known chapter from the Mexican-American War is brought to the screen in this historical drama based on fact. In 1846, shortly before the United States turned its aggressions against Mexico into armed conflict, John Riley (Tom Berenger) and a group of U.S. soldiers crossed the border into Mexico to attend Mass. Riley and his fellow soldiers were Irish nationals who had come to the United States to escape the economic devastation of their homeland, brought on by the Potato Famine. Like many other Irish immigrants, Riley was promised citizenship in exchange for serving a tour of duty in the Army, but the Irish Catholics soon found themselves treated like second-class citizens in the largely Protestant American military. Riley and his men are severely punished for traveling into Mexico, and Riley decides he can no longer abide the United States Army and its treatment of his fellows. Riley engineers an escape from the stockade and the Irish troops travel into Mexico, a peaceful Catholic nation where they believe they will be welcomed. However, as Riley and his men march into the mountains of Mexico, they encounter guerilla leader Cortina (Joaquim de Almeida), who is naturally suspicious of soldiers in U.S. uniforms. The Irish soldiers are taken prisoner and Riley is wounded in the skirmish, but in time Cortina and Riley come to see each other as allies rather than enemies. Riley also falls in love with Marta (Daniela Romo), a Mexican patriot and Cortina's lover. In time, Riley and his men form The Saint Patrick's Battalion and become one of Mexico's most effective fighting units. Tom Berenger served as co-producer for One Man's Hero as well as playing Riley. The film was originally slated for release in the fall of 1998, but was shelved for a year after Orion, the studio which produced the film, was purchased by MGM, who eventually released it in Ireland in August, 1999, and the United States and Mexico later in the fall.