Ivy Sparrow and her big brother Seb discover a city beneath London where ordinary objects have magical powers.

When their grandmother Sylvie is rushed to the hospital, and their house is ransacked, Ivy Sparrow and her annoying big brother Seb find themselves in a completely uncommon world, a secret underground city called Lundinor where ordinary objects have amazing powers. It seems that their family is connected to one of the greatest uncommon treasures of all time-- and the forces of evil are determined to steal it!