User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-5850470-20121217235414/@comment-5897159-20121222120134

i think every book in this series so far has an internal conflict and an external conflict like in the mark of athena, there was annabeth's individual conflict with following the mark, but also the group's mission to stop the two giants, save nico and stop rome from falling i think in the house of hades, there will be the escapade to close the doors of death but also from a bigger point of view, the healing of the rift between the greeks and the romans and in the final book, the gods will unite with the demigods to stop gaea from rising (or along the lines of that, because there isnt much analyzing with the internal and external conflict with so little information given about the last battle)

also im still a little confused with the sacrifice, what does this sacrifice mean and how will it be stopping gaea? i thought the sacrifice was to revive gaea again, one boy one girl right? and what's with the whole thing about percy sacrificing himself to tartarus?