Deep below snowy, cobblestone streets, tucked away in networks of winding subterranean tunnels, 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 ursine troubadour Ernest, the two form an unlikely bond.

A koala impresario stages a grand singing competition for the world's animals in order to save his elegant theater and bring it back to its former glory.