User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-71.231.91.187-20121009193222

A few theories for HoH:

Percy, Annabeth and the crew on the argo 2 fight their way through Tartarus and Greece and make it to the Doors. They can close both sides, but someone must stay behind Tarturus. Annabeth volunteers, but percy wont let her. They need both percy and annabeth, so Hazel volunteers to take their place. Frank protests, but in his mind he knows this must be done. She sacrifices her self and the doors are closed. Nico takes her place as one of the seven. They close the doors and now they must end the war between the camps and together they converge on Gaeas remaining forces in Greece. I back up the theory with Frank when Mars told him that he had to make a decision. A decision Percy couldn't make. What other decision could there be then to sacrificing the one you love to end the biggest war in history? What do you guys think?