Melusine was married off to Oleander, a businessman, against her wishes. Instead of being there for her husband she spends most of her time in an overgrown park, where Melusine feels free and safe. Madame Lapérouse urges her daughter to fulfill her marital duties, but Melusine refuses, accusing her mother of never having understood her - unlike the wood nymph Pythia, who rules over Flora and Fauna as „Queen of the Willows“.
One day Melusine encounters an unexpected visitor in the park : A surveyor charting the site, who tells her the park’s been sold. The Count of Lusignan intends to build a castle there. Melusine manages to win the surveyor onto her and the park’s side so convincingly, that he gives up his job. Oleander regrets not buying the park himself. Madame Lapérouse bursts in saying that someone’s dead: the surveyor threw himself off the park wall. Melusine starts to suspect she has fatal powers.
ACT 2 Melusine urges the plants in the park to fight against threatening distruction. Then calls on Pythia, begging her to do everything she can to stop the castle being built. The nymph of the woods gives Melusine a fishtail, making her irresistibly attractive, so Melusine can seduce all the builders and stop them working, as long as she promises Pythia never to fall in love. When Melusine encounters a group of workmen, she employs her new powers for the first time: the men fall under her spell, including a married architect, and lay down their tools. Melusine’s mission seems to be successful …
ACT 3 A few months later it’s clear: Melusine delayed the castle being built, but couldn’t prevent it. The new building’s about to be inaugurated. Pythia hopes this will give Melusine the chance of seducing the Count of Lusignan to prevent the natural world being completely destroyed. If not, the nymph of the woods sees no future for her community. The Ogre, an old crony of Pythia’s and Melusine’s biological father, is to help her.
At the Count's housewarming party guests grumble about the castle’s curious construction and appearance. When the Count of Lusignan appears at the height of the celebrations, he and Melusine fall in love at first sight. Even words of warning from the architect, out of his mind with love for Melusine, fail to unsettle the Count: He leads Melusine into his castle. Pythia, ceding failure, plans to set fire to the building in revenge.
ACT 4 Melusine and the Count become more tender and intimate. The Count rids Melusine of her fishtail, making her really feel human for the first time. After their first night of love the Count starts feeling uneasy: He fears Melusine’s withdrawing from him and he’ll never understand her. Melusine tells the Count she loves him, painfully aware that she promised Pythia never to fall in love. The Ogre forces Melusine out of her trance, making her face up to the consequences of her liaison: the park’s ecosystem’s permanently destroyed, and Pythia’s set fire to the Count’s castle. He begs his daughter to save herself, but Melusine wants to die in the flames with her beloved. The massive inferno makes a nice change to Madame Lapérouse and Oleander’s daily routine. But when the Ogre appears with two charred bodies they’re horrified to see : The corpse next to the Count is none other than Melusine.