The goddess Persephone has summoned Percy, Thalia and Nico to the Underworld in order to retrieve Hades' powerful sword before it falls into the wrong hands. Easier said than done in a world full of evil daimons, ghosts and ghouls. Not to mention Iapetos - brother of the powerful Titan lord, Kronos. This time the young demigods are really up against it - will Percy manage to return the sword before it's too late? Flip the book over for lots more ancient Greek fun with Terry Deary's brilliant Groovy Greeks.