Tosca is a study in dramatic and musical tension.

     The opera is based on the play written for Sarah Bernhardt by the French dramatist Victorien Sardou who kicked up the stress level using every device known to melodrama. The libretto, a shortened version of the play, condenses the anxiety.

     The story is set in a period of terror: Maria Carolina, the queen of Naples and Sicily, daughter of Maria Theresa of Austria and sister of Marie Antoinette, has recaptured Rome, after Napoleon set up a republic there—the so-called Roman or Parthenopean Republic—and is systematically torturing and executing all even remotely connected with the French, the republic, or modern ideas.

     All this is made more vivid by the realism of the libretto. We know the exact date of the happenings—noon on 17 June 1800 to dawn the following morning, barely sixteen hours, during which we witness torture, an attempted rape, a murder, an execution, and two suicides. The setting is Rome, a city heavy with a history of the church and oppressive regimes. The three locations where the action takes place—the famous church of Sant’Andrea della Valle, the Palazzo Farnese where Queen Maria Carolina is living, and Castel Sant’Angelo, a notorious prison—are real places, within easy walking distance of one another. And several of the characters are based on real people. Angelotti, the escaped prisoner, is almost certainly drawn from Liborio Angelucci, who really was the consul of the Roman Republic. Baron Vitellio Scarpia greatly resembles the real Baron Sciarpa, a mercenary who supported the royalty.

     And, finally, the libretto keeps us on edge by repeatedly forcing us to multitask and divide our attention between two events going on at the same time, sometimes onstage, sometimes offstage.