A brilliant Percy Jackson mini adventure plus Horrible Histories Groovy Greeks - a winning combo for World Book Day!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:It's history with the nasty bits left in! Want to know: Why some groovy Greek girls ran about naked pretending to be bears? Who had the world's first flushing toilet? Why dedicated doctors tasted their patients' ear wax? Discover all the foul facts about the Groovy Greeks - all the gore and more!