On the eve of the Russian Revolution, a performance of "Tosca" is taking place at the opera house. The artists and staff are too engrossed in their work to notice the unrest in the streets. The leading roles are played by Marina Marta and René Areno, who are also lovers. However, Marina has another admirer in Captain Alexander von Harbin. When, during the final performance, the insurgent communists suddenly storm the opera house, Alexander seems to be Marina's last hope…