Despereaux is a young mouse with large ears who is different from his peers. He is brave and curious, often venturing into the world above the mouse kingdom, which is filled with light and adventure. His unique personality leads him to form friendships with unexpected characters, including a princess named Pea. The story unfolds in a dark castle where Despereaux faces challenges that test his courage and loyalty. Themes of love, forgiveness, and the importance of being true to oneself are central to his journey. Ultimately, Despereaux learns that even the smallest creatures can make a big difference.