On Christmas Eve in Victorian London, young Clara Stahlbaum is gifted a locked silver egg from her late mother. Unable to find the key to open it, Clara becomes determined to acquire the missing piece and uncover the secret her mother left behind. At her godfather Drosselmeyer's annual holiday party, Clara's quest leads her to a string with her name on it, which guides her to the key in a parallel world. However, just as she lays her hands on the key, a mysterious mouse snatches it away, prompting Clara to chase after it. As she ventures deeper, she discovers a magical kingdom comprised of four realms: the Land of Snowflakes, the Land of Flowers, the Land of Sweets, and a fourth realm that has fallen under the shadow of a dark conflict.

In this enchanting world, Clara meets a soldier named Phillip, who becomes her companion, along with a group of regents overseeing three of the peaceful realms. The Sugar Plum Fairy, in particular, provides Clara with insight into the delicate balance which holds the realms together and the turmoil that has ensued since her mother's passing, whom they reveal was the queen of the realms. Clara learns that the key to her egg is also crucial to restoring harmony among the realms. She decides to take on the responsibility of her mother's legacy, embarking on an adventure that tests her courage, ingenuity, and determination to bring light back to the unstable world.