Los Angeles Times columnist Steve Lopez (Robert Downey Jr.) takes an inadvertent stroll through Skid Row and discovers Nathaniel Ayers (Jamie Foxx), a mysterious homeless man playing a two-stringed violin. As Lopez digs deeper into Ayers’ life to begin a story for his column, he discovers a musical prodigy with a troubled past which has led him to his present day solitude. Based on a true story. (G)