Annabeth, Jason, Piper and Leo have flown to Camp Jupiter in the magical trireme Argo II, in the company of Coach Gleeson Hedge, action satyr. Percy and his friends Hazel and Frank are more than happy to sign on to the Quest of the Prophecy of Seven, but when Leo unaccountably opens fire on the camp, they are forced to set out straight off and pursued by Roman forces, heading for the forbidden Ancient Lands and a Greek treasure stolen long ago by the Romans. Banishing ghosts and battling monsters, they make their way across the Atlantic to the Mediterranean and Rome, where Annabeth has to go it alone in pursuit of the Mark of Athena, while Jason and Percy overcome their alpha-hero antagonism to take on a pair of giant twins.
Although technically victorious, our heroes begin the next book in the series, The House of Hades, separated, and indeed with Annabeth and Percy literally in Hell, or at least Tartarus.With time running out, and at different speeds for those in and out of Tartarus, the heroes must make their way to the two sides of the Doors of Death in order to close them. En route, Annabeth and Percy must befriend those whom they might have thought implacable foes and learn the meaning of sacrifice. In the mortal world, Frank embraces his inner war god and Hazel is chosen by Hecate to learn to control the Mists. Meanwhile Leo, the perpetual seventh wheel of the quest, finds his destiny and proves that in some ways he is better than Percy Jackson, and Nico di Angelo comes out (which for a popular children's series is pretty huge.)
Riordan continues to combine rollicking adventure, snarky humour and mild horror to good effect. Especially effective is some of the soul-searching in The House of Hades, where Percy is faced with the consequences of his past heroism, not just in the resentment of monsters he has killed, but of those he has left behind and never thought of again (a not uncommon failing in ancient heroes.)
