User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-5938567-20130113185108

Here's another theory. In Percy Jackson and the Olympians, Kronos wanted to get back at the olympians, right? Since Nico helped Hades get him out of his shell, and Percy helped Nico. And Percy also made it possible for Hades to have a throne on Olympus, and a cabin at Camp Half-Blood. Annabeth helped percy with those. Tartarus is in the Underworld, which is Hades' sphere of control. Cerberus bonded with Annabeth in the lightning thief. Maybe, just maybe, Hades will send Cerberus to help protect Percy and Annabeth as an act of appreciation. Just a thought. You are free to state your opinions.