Rosa has always believed there is magic in the world. Or at least, she hopes there is. She lost her parents when she was four, and her aunt and uncle moved into her home not long after, transforming it from a messy place of love and warmth to a cold world of business. Their approach to family is as phony as the plastic grass they sell, keeping Rosa at arm's length and tucking her in at night by locking her in her room.

Now eleven, Rosa's loneliness threatens to overwhelm her. Her only solace is the magic she sees around her, particularly in a cat named Balthazar who comes to--and through--her window. When all the teachers at her school win the lottery and quit their jobs, Rosa's aunt and uncle seize the opportunity to put an evil plan into action. They whisk Rosa away to Venice, intending to abandon her there. Luckily for Rosa, there are cats in Venice--and a laughing boy in a gondola and a family making sure she is fed.

In Rosa's darkest hour, can the magic she's never lost faith in save the day?