▁the ▁main ▁ 7 ▁characters ▁are ▁fighting ▁the ▁main ▁battle . ▁Without ▁their ▁unity , ▁it ▁would ▁be ▁impossible ▁to ▁defeat ▁Ga ia ▁and ▁save ▁the ▁world . ▁ ▁Books ▁ ▁The ▁Lost ▁Hero ▁ ▁The ▁novel ▁begins ▁by ▁introdu cing ▁Jason ▁Grace , ▁Pi per ▁Mc Le an ▁and ▁Leo ▁Val de z , ▁three ▁newly ▁discovered ▁dem ig ods ▁who ▁travel ▁to ▁Camp ▁Half - B lo od ▁in ▁response ▁to ▁a ▁prop he cy , ▁they ▁set ▁off ▁on ▁a ▁quest ▁to ▁prevent ▁the ▁reb irth ▁of ▁the ▁giant ▁king ▁P orph yr ion ▁and ▁rescue ▁Pi per ' s ▁father , ▁who ▁has ▁been ▁kid n apped ▁by ▁another ▁giant , ▁En cel ad us . ▁Jason , ▁who ▁has ▁am nes ia , ▁also ▁begins ▁to ▁remember ▁pieces ▁of ▁his ▁past ▁throughout ▁the ▁book ▁- ▁most ▁important ly , ▁that ▁he ▁comes ▁from ▁a ▁Roman ▁camp ▁for ▁dem ig ods . ▁Camp ▁Half - B lo od ▁resol ves ▁to ▁seek ▁out ▁this ▁other ▁camp ▁both ▁to ▁gain ▁al lies ▁in ▁the ▁fight ▁against ▁Ga ia , ▁the ▁gi ants ' ▁mother ▁and ▁commander , ▁and ▁to ▁locate ▁the ▁missing ▁dem ig od ▁Per cy ▁Jackson ▁the ▁son ▁of ▁P ose id on . ▁ ▁The ▁Son ▁of ▁Ne pt une ▁ ▁The ▁novel ▁opens ▁with ▁Per cy ▁Jackson ▁( stru ck ▁with ▁am nes ia ) ▁discover ing ▁Camp ▁Jup iter ▁and ▁meeting ▁several ▁Roman ▁dem ig ods . ▁After ▁a ▁prop he cy ▁from ▁Mars ,