After that , Percy and Annabeth journey to many dangerous islands , and Annabeth tells Percy many things about how Thalia died and she also mentions her prophecy and tells Percy that he has a choice to make when he becomes 16 years old . Percy and Annabeth journey to many dangerous islands , and Annabeth tells Percy how Thalia died . She also mentions the prophecy and tells Percy that he has a choice to make when he turns sixteen years old .