▁Olymp ians , ▁which ▁detailed ▁the ▁life ▁of ▁modern - day ▁Greek ▁dem ig ods . ▁Ri ord an ▁introdu ces ▁Roman ▁myth ology ▁in ▁his ▁sequ el ▁series ▁as ▁well ▁as ▁several ▁new ▁characters . ▁The ▁first ▁book ▁of ▁the ▁series , ▁The ▁Lost ▁Hero , ▁was ▁published ▁on ▁October ▁ 1 2 , ▁ 2 0 1 0 . ▁The ▁final ▁entry ▁in ▁the ▁series , ▁The ▁Blood ▁of ▁Olymp us , ▁was ▁published ▁on ▁October ▁ 7 , ▁ 2 0 1 4 . ▁ ▁Plot ▁ ▁The ▁Hero es ▁of ▁Olymp us ▁is ▁centered ▁around ▁a ▁prop he cy , ▁introduced ▁in ▁The ▁Last ▁Olymp ian , ▁that ▁predicted ▁seven ▁dem ig ods ▁would ▁un ite ▁to ▁protect ▁the ▁world ▁from ▁an ▁aw ak ening ▁new ▁enemy , ▁Ga ia . ▁Dem ig ods ▁from ▁both ▁the ▁Greek ▁camp , ▁Camp ▁Half - B lo od , ▁and ▁a ▁new found ▁Roman ▁camp , ▁Camp ▁Jup iter , ▁un ite ▁to ▁save ▁the ▁world ▁from ▁being ▁destroyed ▁by ▁the ▁ter ry ifying ▁Earth ▁God dess , ▁Ga ia . ▁The ▁prop he cy ▁reads : ▁ ▁Seven ▁half - blo ods ▁shall ▁answer ▁the ▁call , ▁( H az el ▁Le ves que , ▁Per cy ▁Jackson , ▁Jason ▁Grace , ▁An nab eth ▁Ch ase , ▁Frank ▁Z hang , ▁Leo ▁Val de z , ▁Pi per ▁Mc Le an ) ▁To ▁storm ▁or ▁fire , ▁the ▁world ▁must ▁fall . ▁( Le o ' s ▁fire ▁powers