In Mozart's opera Cosi fan tutte the sisters Dorabella and Firodiligi sing two rather different duets in Mozart's school for lovers - the first duet is all about loyalty to their loved ones, and the second a betrayal duet in which they encourage each other to choose a lover. And how is all this expressed in the music that Mozart wrote? David Sebba, together with Anat Czarny and Yael Levita, will reveal to you in an episode of A Moment of Opera.