When 10 year old Meggie hears Wanda announce that she's setting up a summer business selling miracles, Meggie thinks Wanda's finally gone off the deep end. But that's before Meggie's sister is born way too early. Now, the doctors aren't sure if the baby will live and mom and dad are spending all their time at the hospital. Suddenly, Wanda's miracles don't look so crazy anymore. But Wanda doesn't just sell Meggie a Miracle. She wants an assistant. If Meggie wants to save her sister, she'll have to first help Wanda transform an elderly neighbor into Madame Butterfly and get her a gig singing at Carnegie Hall. Coordinating a concert at Carnegie Hall isn't as simple as it sounds, but if Meggie can't pull it off, she'll never learn the secret to saving her little sister or making miracles.