Letters from Son My is based on the story of Lt. William Calley (renamed Peter Cage in the film). Calley was the officer in charge and deemed responsible for the infamous My Lai Massacre which happened during the Vietnam War when almost the entire village of Son My (the film was made on location at the village) was slaughtered by American troops. Calley recently returned to Vietnam to apologise for his actions all those years ago and the movie portrays the period of his life leading up to this with brief flashbacks from the war also included.