<P> On their journey , they encounter Phineas , the blind human who helped Jason , leader of the Argonauts on his journey , and befriend a harpy named Ella that supposedly torments him . They also see the three Cyclopes that Jason Grace , Piper McLean , and Leo Valdez encountered in The Lost Hero . During the trip , the trio learns that the goddess Gaea is awakening from several millennia of slumber with a plan to destroy the gods and the world along with them . Her seven Giant children are being woken , each of whom is matched to fight their counterpart god . Each Giant has the skills to oppose one god and they can only be defeated if the gods and the demigods join forces . This proves to be difficult . Percy and his friends manage to defeat the Alaskan Giant and save Camp Jupiter from destruction . During their journey , Hazel and Frank become true heroes who know how to use their powers and have self - confidence . Percy regains his memory on their return to Camp Jupiter and finds an army of monsters ( including Stheno , Euryale , and the three Cyclopes ) led by Polybotes attacking it . Percy successfully defeats him with the help of Terminus , his Cyclops half - brother , Tyson and the hellhound , Mrs. O'Leary . At the end of the book , the Greek airship , Argo II arrives setting up the plot for The Mark of Athena . </P>
when does percy get his memory back in the son of neptune
on their return to Camp Jupiter