User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4521561-20121224015716

As shown in The Demigod Files, Ethan Nakamura used Hades' Unfinished sword to release Iapetus from Tartarus. Now Ethan is a demigod of a minor god and he used the unfinshed weapon to release a powerful titan from Tartarus.

Now getting to my point Hades is a powerful god who has the finished weapon able to raise an army of the undead as shown in The Last Olympian. So why can't Hades use his sword to release Percy and Annabeth from Tartarus.

All Nico has to do is regain his strengh and Shadow Travel to the Underworld and beg his father to us his power to release them. Poseidon and Athena must know thier children have fallen into Tartarus and demand Zeus and Hades to release them.