Deep below snowy, cobblestone streets lives a civilization of hardworking mice, terrified of the bears who live above ground. Unlike her fellow mice, Celestine is an artist and a dreamer, and when she nearly ends up as breakfast for a grumpy bear named Ernest, the two form an unlikely friendship.
When the roof leaks, Ernest the bear plays his violin and Celestine the mouse sings in the street to earn money for repairs, but they find other uses for it.
Ernest the bear is willing to help when his mouse friend Celestine breaks a cup, but she wants to take the responsibility for cleaning up her mess herself.
