Mario Castelnuovo-Tedesco (Xander Berkeley of “The Walking Dead”) was the composer of more than 200 Hollywood films in the 1940s and 1950s. Mario went on to mentor some of film music’s greatest composers, including John Williams, Randy Newman, Henry Mancini, Jerry Goldsmith, and Andre Previn. “The Maestro” follows budding film composer Jerry Herst (Leo Marks) as he moves to Hollywood after World War II to study with infamous master teacher Castelnuovo-Tedesco. The film is based on real letters between the two men. An array of film and music luminaries — Gene Kelly, Cyd Charisse, Nelson Riddle, Igor Stravinsky, Stanley Kubrick — are portrayed onscreen as they enter and exit the composer’s orbit. The cast includes native St. Louisan Sarah Clarke (as Castelnuovo-Tedesco’s wife), William Russ, Mackenzie Astin, and the late Jon Polito.