This the the 4th book in the Percy Jackson and the Olympians Series by Rick Riordan. It is the summer before Percy turns 15 and he has yet another school orientation before heading off to camp. Again, monsters disrupt his orientation and the school is left believing he firebombed a cheerleader. Percy and Annabeth return to camp, only to find that Kronos is growing stronger and the Titans' revolt is imminent, Grover is about to lose his searchers' license, Clarisse is capable of being almost nice, and Annabeth must lead the others on a quest through the labyrinth if they are to have any hope of saving the camp from Luke's invasion. So, Percy, Annabeth, Grover, and Tyson head into the labyrinth, but they soon find they can't find their way without a mortal guide, so Percy calls on his friend Rachel Elizabeth Dare, which does not make Annabeth happy. Also, there is still the problem of Nico, son of Hades, who still blames Percy for the death of his sister. Nico could be an ally to the camp or he could be a very powerful enemy, and he is being influenced by a dangerous spirit.
Lives are at stake, as usual, and there is the added "girl drama" with both Annabeth and Rachel possibly wanting to be more than friends with Percy, not to mention an encounter with Calypso.
Yet again, the allusions to Greek mythology add to the fun. The big battle fulfilling the prophecy will happen in the fifth and final book in the series, available now, though I have not yet read it.