User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-7003590-20130312002108/@comment-3146930-20130314044053

The covers normally reveal at least one or two important plot points. The Lost Hero showed Festus and if you know the building in back, you know they would be going to Quebec. The Son of Neptune showed Percy surrounded by ice with a glacier falling apart and Percy with the Eagle; once again we know that it takes place up north and the Eagle is very important. The Mark of Athena showed Percy and Jason about to do battle, even if the fight in the book was sort of weak and wasn't really important. On the other hand, there are different covers in every country so we can kind of piece together a bunch depending on what the covers show