Sam and Lily have a typical sibling relationship; Lily (the younger sister) annoys Sam, and Sam always gets blamed for anything Lily does wrong. The girls are spending the summer with their grandparents, and Sam is not excited to spend the whole summer hanging out with Lily. So when she meets their neighbor, a boy named Marcus, she's excited to have someone her own age to hang out with, especially when she discovers that he also loves to read. The three of them are hanging out when Lily runs off into the woods behind the house. Scared that she will get lost, Marcus and Sam run after her. Once they find her, they start talking for a while, when Lily suddenly disappears into thin air almost as if something in the woods grabbed her. Sam quickly tells her grandparents, and she expects them to call the police.  Instead they act as if they already knew that this might happen! But when Sam and Marcus find a mysterious note telling them how to get Lily back, they know they must work together to save Lily before it is too late.