User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-5247339-20130622090134/@comment-7742465-20130622174452

That... Would actually sort of make sense. In the first chapter of HoH, Hazel says Arion is going to help them, and Arion is a son of Neptune... And maybe the giant turtle is one of Keto's sea monsters, and Neptune wants it destroyed... Or something like that.