Circleen is moving to town with her two friends Ingolf and Fredrik. They meet the city mouse Sidse who knows the secrets of the city and who lives alone with her granddad and her kid brother Viktor on a ship in the harbour. And then there is Hassan, a turkish mouse, and his family, helping out at the greengrocer’s to get some feta. Sidse shows her new pals Circleen and Fredrik the city, riding around in various ways – in a rollerskate, a motorbike, a toyplane or a railway train. But the city has dangers. A big rat lives in the sewers drain and one day it appears…….