It’s a simple story: The Count hangs out in a music hall, where he falls in love with singer Sylvia. But since she performs in cafés and theaters — a social ranking just a little bit above “whore” — his father won’t let them marry. In The Gypsy Princess, or Die Csárdásfürstin, Hungarian composer Imre Kalman has his characters sing in a style that melds Hungarian folk songs and Viennese waltzes, which was at the top of the pops back in the early 20th century. It turned out to be his most successful operetta. Spoiler alert: The story ends happily when the young Count learns that his father was in the same situation when he married the Count’s mother, a former singer. Opera Circle continues to explore repertoire beyond the warhorses most companies use to build their seasons with The Gypsy Princess at 7:30 tonight and 3 p.m. Sunday at the Bohemian National Hall (4939 Broadway Ave., 216.441.2822). Tickets: $10-$55. — Michael Gill