In simple words this book is simply mind-blowing. This is the 4th book in the Heroes of Olympus series and like the previous three this book was great. Percy and Annabeth have fallen in Tartarus - a place from which no one has ever returned alive.The book's storyline is quite gripping.Fans of Rick Riordan will simply devour this book. The crew on the Argo 2 go to places like Venice, face the minions of Gaia together and carry on to Epirus. The best part is that no matter what happens all the seven demigods are united. Though Nico is frighteningly silent and grim, he too helps the demigods to a great extent. Readers also get to meet two old friends-I'll not tell you who they are now. The way Percabeth survive in Tartarus....Its simply awesome. So I guess this book will be on my list of Super-Cool Books.