Act I
On the shore of a lake in the middle of the woods, three wood-sprites are teasing Vodník, the water goblin, with a game of catch-me-if-you-can. Each time, they evade his grasp. Rusalka, a water-nymph, is Vodník’s daughter. She is sad as she no longer feels at home in the water. She longs to escape and assume a human form, with a human soul, so that she could become visible to a prince she has seen hunting near the lake and thus be able to experience human love.
Rusalka asks her father for a solution. Despite her initial warnings, he takes her to see the witch, Ježibaba. Rusalka begs the witch to transform her. Ježibaba agrees, but in exchange, Rusalka will have to sacrifice her voice. Furthermore, Ježibaba’s help comes with a curse: if Rusalka fails to win the prince’s heart, she will be banished and condemned to wander between life and death as a spirit for all eternity. Her beloved prince will suffer damnation. Rusalka agrees to the terms.
Out hunting, on the trail of a white doe, the prince and the hunter come across Rusalka. The prince is instantly captivated. He brings her to his castle.
Act II
At the prince’s castle, preparations are underway for a ball. The kitchen boy tells the gamekeeper that the prince wants to marry a woman he brought back with him from the forest the week before. According to the kitchen boy, the prince has already fallen out of love with Rusalka.
The rumours circulating at court prove to be true: the prince no longer loves Rusalka. He is repulsed by her cold, clammy body and inexplicable silence. A foreign princess asks the prince to take better care of his guests. After the prince coldly tells Rusalka to ready herself for the ball, the prince and the princess go off together to join the other guests. Rusalka is left behind, alone.
While the guests dance and make merry at the ball, Vodník comes and laments Rusalka’s fate. In his presence, Rusalka regains her voice and complains of her suffering. The foreign princess has won the heart of the prince, who has rejected Rusalka. Vodník threatens him. He will never be able to escape her embrace. The princess, too, abandons the prince. Vodník escorts Rusalka back into the depths.
Act III
Back in the woods, on the shore of the lake, Rusalka laments her fate. Ježibaba appears before her and offers her a way out: if Rusalka kills the prince, she may return to the watery world. Rusalka refuses her offer as she would rather submit to her fate than to kill the man she loves. Rusalka is ostracised by the other water-nymphs.
The gamekeeper and the kitchen boy visit Ježibaba to ask her advice about the prince, who is wandering in despair. She laughs at them and they are frightened. When they blame Rusalka for the prince's state, the water goblin Vodník appears. He reminds them that it was actually the prince who abandoned her. Vodník swears revenge. The three wood-sprites begin to sing and dance. Vodník tells them that Rusalka is condemned to suffer and she has been banished by her sisters.
The prince is desperately searching for his exiled love. He repents and asks Rusalka for a kiss. She warns him that it will be fatal but the prince insists. After the kiss, he dies in her arms. Rusalka thanks the Prince for letting her experience human love and commends his soul to God. She then returns to her place in the depths of the lake as a bludička, a will-o’-the-wisp, a demon condemned never to live nor die that emerges only to lure humans to a watery grave.