The House of Hades

The House of Hades is the fourth book in Rick Riordan Heroes of Olympus series.  It is about when Piper,Jason,Leo, Hazel and Frank to go to the doors of death. Nico is there because he promised Percy to  take the others to the doors of death after he and Annabeth were fallen into Tartarus. When Leo is on duty with Hazel and Nico. Hazel tells them to wait on the ship because she sees Arion her horse. When she gets on Arion's back he speeds into a fog. In the fog there is Hecate she offers Hazel tea. Annabeth and Percy are struggling in Tartarus. Annabeth remembers reading that in Tartarus there is a River of Fire it has healing properties. When they are get to the river Annabeth goes first and has to put her hand because Percy doesn't have the strength to do it.  After she is done helping Percy she realizes that he is getting his color back and back to his usually self.