In order to save their kingdom from evil rodents, Sebastian (Drake Bell) and Samantha (Miranda Cosgrove) are sent on a quest by the King of Rodencia (Jon Lovitz) and the wise Wizard Dalliwog (Tom Arnold) to obtain a legendary magic crystal that has the power to defeat the rodents. With the help of two trustworthy knights (Carey Elwes and Jon Heder), they venture deep into the forest and enter a forbidden world of giants in order to accomplish their mission and restore order to the kingdom.