The Lost Hero (heroes Of Olympus Book 1) (Rick Riordan)

When Jason, Piper and Leo crash land at Camp Half-Blood, they have no idea what to expect. Apparently this is the only safe place for children of the Greek Gods - despite the monsters roaming the woods and demigods practising archery with flaming arrows and explosives. But rumours of a terrible curse - and a missing hero - are flying around camp.