This adventure begins with Mia wearing her mother's new hat, without permission, while playing on the roof of her house.
Without warning, a torrential downpour washes Mia down the drainpipe.
She barely manages to avoid being swept into the sewer, but her mother's hat slips away.
Down the sewer it goes, where it is commandeered by the evil rat, Romaine and his wretched cousins.
Mia must get the hat back from Romaine or she'll be in some kind of trouble.
With help, Mia must find enough "sparklies" to trade for her mother's hat. But hurry--mother will be calling her home soon.