User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4649443-20130614032639

What I think will happen in Books 4 and 5:

On their way to the House, the group meets Grover(and Hedge bows down to him, 'coz Grover led the nature spirits to a big war and stuff...), who says he can feel Pan regenerating, so he's looking for him. Again.

Annabeth and Percy fight through a horde of monsters, solve puzzles, fight this big guy with a helmet.

When both parties reach the Doors, Annabeth and Pecy find an inscription talking about needing one of the blood of Athena/Minerva on the Tartarus side and one with the blood of Poseidon/Neptune on the other. This is where the big sacrifice Phineas and Mars mentioned comes in. Percy wouldn't be able to do it, except for Frank's duty speech. So Annabeth gets left behind in Tartarus....

For some reason, the two camps become teammates, then ride their various vehicles and whatevers to follow the group to Greece.

Just when Percy is about to get on the Argo II, Calypso makes an appearance.

End of Book 4

So Book 5 starts of with the group going to Mount Olympus to stop Gaea. Of course, loads of adventures happen in between. So while these stuff happen, Percy and Calypso grow closer(obviously).

Grover splits from the group with Hedge halfway there to look for Pan.

Just a day before they get to Greece Gaea sends him a dream showing him that Annabeth is alive. So when they get there, epic battle happens, and then Percy sees Annabeth about to be stabbed by this big giant, and blocks the spear with his own body. Annabeth survives, but Percy is fatally wounded, and his blood may have helped Gaea rise...so now, both camps unite and go to war and stuff.

Pan arrives, defeats Gaea, and resurrects Percy using his Nature healing skills.

Darkcloud swoops in, steals Calypso from Percy, Annabeth and Percy get together again.

The End(or is it!?)