The Lost — Cindy Cipriano

Calum Ranson is now closer than ever to finding his lost cousin Finley: he knows where he is, he just doesn't know how to get there. Stuck in the Void between the world of the living and the Underworld, Finley needs to get home soon before he is changed forever. It's up to Calum and his friend Laurel to figure out how to free him. 

Adding to the challenge, Calum can no longer turn to his other cousin and best friend, Hagen, who has become mysteriously close to one of their school's biggest bullies, Riley Sloan. Why has Hagen suddenly started treating Riley as his girlfriend when she used to be his enemy? And can Calum succeed in saving Finley without Hagen's help? 

From studying to school dances, field trips to first kisses, the third book of the Sidhe depicts a typical middle school experience, peppered with magic, faeries, and truly heroic deeds.