Heroes of Olympus - The Lost Hero by Rick Riordan

Old enemies awaken as camp half-blood’s new arrivals prepare for war. 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. It seems Jason, Piper and Leo are the chosen ones to embark on a terrifying new quest, which they must complete by the winter solstice in just four days time. Can the trio succeed on this deadly mission – and what must they sacrifice in order to survive?