Mary Catherine "MK" (voiced by Amanda Seyfried), a young girl who just lost her mother, took a taxi to a large forest that is almost isolated from the world. Here lives her father, a scientist who firmly believes that there are dwarves living in the forest. In order to find these little creatures, he is willing to sacrifice his family and marriage. The day Mary arrived happened to be the summer solstice and the full moon, a special day that only happens once a hundred years. Queen Tara (voiced by Beyoncé Knowles), the guardian of the forest, who is surrounded by the green and peaceful forest, will choose an heir on this day, but their mortal enemy, the Boggan, will try every means to prevent the birth of the heir, so that they can smoothly bring the breath of decay and death to every corner of the forest. Mary, who does not believe her father's statement, is accidentally involved in the survival dispute between the two dwarves, and she and several warriors of the forest guardian shoulder the responsibility of defending the forest...