▁Olymp us ” ▁and ▁the ▁beginning ▁of ▁“ The ▁H idden ▁Oracle ,” ▁the ▁first ▁book ▁in ▁the ▁next ▁series , ▁the ▁Tri als ▁of ▁Apol lo . ▁▁ ▁G le es on ▁H edge : ▁An ▁old ▁sat yr , ▁formerly ▁a ▁coach ▁at ▁the ▁W ilder ness ▁School . ▁H edge ' s ▁first ▁child ▁is ▁born ▁during ▁the ▁final ▁book ▁of ▁the ▁series . ▁ ▁Th alia ▁Grace : ▁Th alia ▁is ▁Jason ▁Grace ' s ▁bi ological ▁sister , ▁but ▁a ▁daughter ▁of ▁Ze us ▁rather ▁than ▁Jup iter ▁( J up iter ▁and ▁Ze us ▁are ▁the ▁same ▁god ▁in ▁different ▁aspects , ▁making ▁Jason ▁a ▁child ▁of ▁Rome ▁and ▁Th alia ▁a ▁child ▁of ▁Greece ). ▁ ▁T ys on : ▁T ys on ▁is ▁a ▁cy clo ps , ▁the ▁half - bro ther ▁of ▁Per cy ▁ ▁Rach el ▁Elizabeth ▁D are : ▁Camp ▁Half - B lo od ' s ▁oracle . ▁Rach el ▁is ▁not ▁a ▁dem ig od ▁or ▁a ▁legacy ; ▁she ▁is ▁a ▁regular ▁mort al ▁human ▁who ▁was ▁born ▁with ▁the ▁gift ▁to ▁see ▁through ▁the ▁M ist . ▁She ▁is ▁the ▁current ▁Oracle , ▁being ▁a ▁vessel ▁for ▁the ▁Spirit ▁of ▁Del phi . ▁ ▁Gro ver ▁Under wood : ▁Per cy ' s ▁best ▁friend , ▁a ▁sat yr ; ▁he ▁and ▁Per cy ▁have ▁an ▁em path y ▁link ▁that ▁allows ▁them ▁to ▁sense ▁one ▁another . ▁Also , ▁Gro ver ▁Under wood ▁is ▁gift ed