Jack might be the only kid in the world who's dreading summer. But he's got a good reason: summer is when his single mom takes a second job and leaves him at home to watch his autistic kid sister, Maddy. It's a lot of responsibility, and it's boring, too, because Maddy doesn't talk. Ever. But then, one day at the flea market, Maddy does talk to tell Jack to trade their mom's car for a box of mysterious seeds.