Milly is an ordinary cat. Fluffier than most, certainly, but otherwise very ordinary. Or that's what she thinks. But she has a destiny, one that is carved into a legend on the ancient walls of a temple in another world, ruled by magical mice but threatened by an army of evil rats. The rats will do anything to stop the legend coming true, and when Milly is attacked one peaceful afternoon near her home, she only survives with the help of a bedraggled young mouse who appears from nowhere. He tells her the rats will be back and that they will not rest until she's dead. Her only hope is to return with the mouse to his world and fulfill her destiny.