▁The ▁Sea ▁of ▁Mon sters , ▁Per cy , ▁An nab eth , ▁and ▁T ys on ▁run ▁into ▁the ▁Gray ▁Sister s ▁who ▁are ▁in ▁the ▁form ▁of ▁three ▁tax i ▁drivers . ▁During ▁the ▁Gray ▁Sister s ' ▁argument , ▁Per cy ▁man ages ▁to ▁grab ▁their ▁eye ▁and ▁demand ▁the ▁location ▁of ▁which ▁they ▁had ▁mentioned . ▁They ▁tell ▁him ▁ 3 0 , ▁ 3 1 , ▁ 7 5 , ▁ 1 2 ▁which ▁Per cy ▁didn ' t ▁understand . ▁He ▁however ▁gave ▁the ▁eye ▁to ▁W asp ▁and ▁they ▁drop ▁the ▁three ▁off ▁at ▁Camp ▁Half - B lo od . ▁Later ▁at ▁the ▁camp fire , ▁Per cy ▁figures ▁out ▁that ▁the ▁numbers ▁were ▁used ▁for ▁longitude ▁and ▁latitude ▁which ▁leads ▁to ▁the ▁Sea ▁of ▁Mon sters . ▁In ▁the ▁film ▁adaptation , ▁the ▁Gray ▁Sister s ▁are ▁port rayed ▁by ▁Mary ▁Bird song , ▁Y v ette ▁N icole ▁Brown , ▁and ▁Miss i ▁P yle . ▁ ▁Har py ▁– ▁Wing ed ▁spirits ▁of ▁sudden , ▁sharp ▁g ust s ▁of ▁wind . ▁They ▁were ▁known ▁as ▁the ▁" H ounds ▁of ▁Ze us " ▁and ▁were ▁dispatch ed ▁by ▁the ▁god ▁to ▁sn atch ▁away ▁( h arp az ô ) ▁people ▁and ▁things ▁from ▁the ▁Earth . ▁Sud den , ▁myster ious ▁disappear ances ▁were ▁often ▁attributed ▁to ▁the ▁Har p ies . ▁There ▁are ▁three ▁Har p ies ▁that ▁were ▁created ▁by ▁Ze us . ▁They ▁work ▁in ▁Camp ▁Half