''Cain has established a formidable reputation of furious pace, harsh and masterful realism, tough, raw speech right out of the mouths of the people'' SATURDAY REVIEWSerenade is the story of the eternal triangle - with a difference. John Howard Sharp is an American opera singer down on his luck, having just bombed in Rigoletto in Mexico City when he first encounters the beautiful Mexican-Indian prostitute called Juana. Miraculously, she offers him the chance to rebuild his career in Hollywood and New York but then Winston Hawes, the young, rich and well-connected conductor who had first launched Sharp, comes back into his life with terrible consequences.