When Callas sang Tosca at Covent Garden in 1964, she could not have known how crucial it would prove to her career and her life. It was the last role she performed on stage: a huge success and a high point in twentieth century opera, but it marked the beginning of the end for the diva. Loss of nerve, voice and love were to follow. Franco Zeffirelli"s legendary Tosca and the production"s resonance with Callas"s own extraordinary story are the focus of this documentary, which draws on rare archive footage and a wealth of documents and stills. Zeffirelli, Tito Gobbi (her Scarpia) and Placido Domingo are among the contributors.