House of Hades by Rick Riordan

Heroes of Olympus series. Puffin, 2013. ISBN: 9780141339191.
(Age: 12+) In this latest adventure of the intrepid and dauntless demi-gods, Percy and his girlfriend Annabeth are trapped trekking through the Underworld, pandemonium reigns in the form of an escalating feud between the Greek and Roman versions of the immortals and most dire of all, the earth is under threat from Gaia (Earth) the most ancient, powerful and malignant goddess of all.
As Percy (son of Poseidon, for those who don't know) and Annabeth (daughter of Athena) combat monsters and dark forces, the rest of the band of seven are struggling with their part of the fateful mission to save the world. They are Leo (son of Hephaestus), Frank (son of Mars), Piper (daughter of Aphrodite), Hazel (daughter of Pluto) and Jason (son of Jupiter) and each brings to the band of comrades their own special attributes or demi-god powers.
"Seven half-bloods shall answer the call,
To storm or fire, the world must fall,
An oath to keep with a final breath,
And foes bear arm to the Doors of Death."
The wonderful juxtaposition of teenager/demi-god is one of the most significant devices in the books. As normal as teenagers can be with their anguish over boy/girl relationships, being popular and so on, these teenagers deal with a rigid definition of their own half-blood heritage.
Moments of humour break the tension and the whole plot is believably and proficiently executed as time races away and the band of semi-divine warriors each face their own demons.
Devotees will have already scoffed this up upon release but definitely worthy of a place on the shelves for readers 12 and up.
Sue Warren