In a season stuffed with nutcrackers and Scrooges and sleigh rides, OPERA San Antonio presents a 45-minute one-act opera about some of the less-explored characters of the Christmas story: the three wise men. In Gian Carlo Menotti’s opera Amahl and the Night Visitors, the gold, frankincense and myrrh-bearing men — on their way to the famous stable — visit a young shepherd boy named Amahl and his mother.