Tommy was one of the first albums I had, so I knew the story before I saw the film and absolutely love both.
Basically, young Tommy's dad is "killed" in the war, and he goes deaf dumb and blind from the trauma. His step dad (Ollie Reed) is a bastard. Uncle Ernie abuses him, Cousin Kevin bullies him and Reed takes him to the Acid Queen to see if drugs will help. Reed is frustrated with the boy who stares at himself in the mirror all day. When his dad miraculously turns up alive, Reed kills him (this bit isn't referenced in the album lyrics, just the film). Tommy's unique talent is to play pinball by instinct, beating Elton John's Pinball Wizard. He becomes a cult figure, which his family try to cash in on with tours and holiday camps. In a fit of anger, Reed smashes Tommy's mirror causing him to snap out of his afflictions with the final "I'm free" song, and he becomes even more of a messiah-like figure. His followers riot tearing down the camp.