Rosa's Grandma is sick in bed, and the big chair in the living room is usually empty now. So is the family's money jar. Rosa is worried: how can she help? One thing that makes Grandma feel better is hearing Rosa play music with her friends. She says it makes her feel like a girl again, dancing at a party. This gives Rosa an idea. If Grandma loves their music, maybe people would pay to hear them! And that's the beginning of the Oak Street Band.