A realm divided between a land of fairies and light, and a land of bog creatures and darkness, living in the dark forest. Primrose flowers, which are a crucial ingredient to love potions, mark the border between the lands. Marianne is a fairy princess and heir to the throne of the Fairy Kingdom, and is engaged to be married to Roland, a handsome warrior who breaks her heart when she discovers him kissing another fairy on their wedding day. Scorned, Marianne vows to never fall in love again.
Sometime later, her sister Dawn, who frequently says she is in love, is distraught regarding the upcoming Spring Ball over which boy she could meet there. Her best friend Sunny, an elf who has a crush on Dawn, tries to cheer her up with a song, but they are nearly devoured by a giant lizard before a hardened Marianne rescues them. Sunny, having fallen through the border of the dark forest, finds a Primrose petal, which he subsequently hides when fleeing the forest.
At the ball, Roland tries to assert his intention to marry Marianne, who refuses and humiliates him out of the dance. He encounters Sunny and tricks him into returning to the dark forest to convince the Sugar Plum Fairy, who had been captured years ago by the Bog King, to create the love potion. Sunny acquires the petal he had hidden and with the help of a curious imp, ventures into Bog's castle, eventually finding the fairy and promising to free her in exchange for the love potion.
Their escape rouses Bog, who manages to recapture the Sugar Plum Fairy while Sunny escapes, followed by the imp, and Bog is enraged when he learns that Sunny has a vial of love potion. Sunny returns to the ball and tries to hit Dawn with the love potion during his musical number. Bog interrupts the celebrations and captures Dawn just as she is sprayed by the love potion and the imp steals it in order to spread it throughout the forest. Bog orders them to deliver the potion to him by moondown or he would harm Dawn. Defying her father's order, Marianne flies off after her sister while he grants Roland a small army to head off on foot to Bog's castle.
Meanwhile, Dawn falls in love with him due to the potion, and Bog has her imprisoned for his own sanity. Marianne arrives and fights with Bog to return her sister. When she realizes the severity of the situation, the two of them begin to find common interests. When they consult the Sugar Plum Fairy for an antidote, she explains that true love will negate the effects of the potion, recounting a time where Bog fell in love with another female in the forest who left him despite his use of the love potion on her, as she was in love with someone else at the time he used the potion on her. A mutual attraction begins to develop between Marianne and Bog, but it is only Bog's mother who sees it.
Sunny recovers the potion from the imp and gives it to Roland as they march on to the castle. Bog sees this and suspects that Marianne had set him up, breaking his heart again as he leaves her stranded in a spider web. She escapes and joins in the battle taking place at the castle. Sunny frees the Sugar Plum Fairy, Dawn, and (at the Sugar Plum Fairy's insistence) the love-stricken forest creatures that the imp had hit with the love potion.
In the escape, Bog seemingly sacrifices himself by holding the mouth of his den open long enough for everyone to escape. He survives, to Marianne's relief, and Sunny reveals his true feelings to Dawn, who then reciprocates them, breaking the love potion's spell over her and they kiss, to her father's surprise. Roland sprays Marianne with the love potion, who pretends to fall in love with him, only to suddenly punch him and send him off the chasm, being hit by the love potion in the process.
Marianne and Bog, at the insistence of Dawn and his mother, finally admit their feelings for each other and kiss.