For a century, Swan Lake has been the ballet, the source of the visual cliches that say “ballet” to the non-ballet public. But it was a flop, a victim of poor staging and choreography, when it premiered at the Bolshoi Theater in March 1877, and was forgotten during Tchaikovsky’s lifetime. He laid his score aside, and his plans to revise it and extract an orchestral suite were unfulfilled at his death. Nobody now knows exactly what the “original” version was like (if there can be said to be one, since there were changes made even during the brief run of performances). The ballet score as we know it was done posthumously by other hands.
The ballet is constructed in four scenes. In the first, a prince celebrates his coming of age at his palace, in anticipation of a ball the following night where he is to choose his bride. In the second scene, a late-night hunting expedition takes the prince to a lake where a sorcerer has cast a spell on young maidens, turning them into swans for no particularly good reason. They can take their human form only between midnight and dawn, which is when the prince finds them and, this being ballet, immediately falls in love with swan-maiden Odette. The third scene is the ball, where the sorcerer appears with his daughter, Odile, to whom the prince then swears undying love because the sorcerer has transformed her to look like Odette. The truth is revealed in the final scene at the lake, where the spell is broken and the prince and Odette die a romantic death together or live happily ever after, depending on which version is being staged. The Waltz is danced by local villagers in the first scene.
— Howard Posner