In a mystical realm, the Fairy Kingdom and the Dark Forest exist in a delicate balance. Heartbroken on her wedding day, fairy princess Marianne (Maya Rudolph) vows to never surrender to love again after catching her fiancé Roland (Elijah Kelley) in a compromising situation. Meanwhile, the Bog King, deeply cynical and troubled, grapples with his own sentiments, much to the annoyance of his mother, Griselda.
When Marianne's sister, Dawn, and her elf companion, Sunny (Kristin Chenoweth), find themselves on the brink of being eaten by a gigantic lizard, it's Marianne who swoops in to save the day. In the aftermath of this close call, Sunny discovers a primrose petal but keeps it hidden, unaware of its significance in the events to come. At the Spring Ball, Roland tries to win back Marianne's affection, but her anger sends him away. Seeking advice from his warriors, they jokingly suggest a love potion may do the trick. This puts him on a fateful encounter with Sunny, whose unreturned love for Dawn parallels his own despair over Marianne.
Eager to secure the love potion for both himself and Sunny, Roland convinces her to enter the Dark Forest in search of the coveted elixir. Guided by a mischievous Imp, Sunny traverses the perilous landscape, eventually arriving at the lair of the enigmatic Sugar Plum Fairy, who is imprisoned. She agrees to create the love potion if Sunny helps her escape. However, the Bog King soon captures Sugar Plum again and demands the love potion under duress.
Despite her father's warnings, Marianne defies authority and rushes to find her sister, while Roland gathers a small army to confront the Bog King. The potion soon takes effect, leading to Dawn developing an inexplicable affection for the Bog King himself. As Marianne battles this unexpected twist, she starts to uncover a surprising connection with her sister's captor.
With the help of Sugar Plum, they learn that true love is the only antidote to the potion's effects. As Marianne and the Bog King begin to understand one another, a mutual attraction blooms, although only Griselda observes this budding romance. Meanwhile, Roland, together with Sunny, sets out on a perilous journey to the castle with the potion in tow, which alters their relations forever. The Bog King's world shatters when he sees Sunny giving the potion to Roland, leaving him feeling betrayed and heartbroken as Marianne cleverly escapes from a web created by a spider.
Refusing to be thwarted, Marianne joins her allies to confront the challenges within the castle. Amidst the chaos, Sunny seizes a moment to free Sugar Plum, Dawn, and other enchanted creatures ensnared by the Imp’s malicious potion. In a brave bid to protect his friends, the Bog King holds open his den's entrance, ensuring safe passage for all. Though they emerge battered but resilient, he earns Marianne's gratitude. As Sunny gathers the courage to express his feelings to Dawn and they share a soft kiss, it becomes evident that the Bog King musters the bravery to confess his emotions to Marianne, leading to a poignant romance blossoming between them.
