During a snowy Christmas Eve, siblings Tyltyl and Mytyl are at home, expecting the usual holiday excitement. Their mother, however, is ill, and the night keeps them awake. Suddenly, a mercurial magical spirit named Berylune bursts through the window, telling them that our world is not the only one that exists. Guided by Berylune and joined by various spirits and their now‑humanoid pets, the brothers set out on a quest to find the blue bird of happiness and cure their mother. Along the journey they travel to strange and wondrous places, and ultimately confront the spirit of darkness in order to achieve their elusive goal.