When Maisie's mom gives her an old phone, Maisie can't believe her luck--finally, she can keep up with everyone at school! Unfortunately, her mom also tells her that the whole family will be moving to spend the summer taking care of Maisie's great-aunt Hazel. Maisie's only getting a phone because she'll be responsible for her younger siblings during the entire trip. With that, Maisie is ready to give the phone back.
 
Then the first puzzling text comes in.
 
Between the mystery texts and a not-completely-blank book from Great-Aunt Hazel, Maisie finds herself thrown into the world of moonleapers. Will she be able to learn more about the secretive group, and--gulp--help them accomplish their crucial mission in time?