New York Times #1 bestselling authors Rick Riordan and Mark Oshiro collaborate again on a new adventure in which demigod Nico di Angelo teams up with his half-sister Hazel Levesque to protect . . . monsters? A few months after returning from the depths of Tartarus, demigods Nico di Angelo and Will Solace agree to join Nico's half-sister Hazel Levesque at Camp Jupiter on the West Coast. She needs their help in managing a situation that the boys inadvertently brought about: the demigods showed the monsters of the Underworld that they have options; they don’t have to be evil. Now some of those monsters have taken up residence at Camp Jupiter to seek refuge. Nico and Will are on site, assisting Hazel when one by one monsters start disappearing from camp. A mysterious dark force is at work, and its plan is to punish all monsters for their past crimes. Things only get worse when Nico, Will, and Hazel learn that they’re all connected to it . . .

Annabeth is terrified. Just when she's about to be reunited with Percy—after six months of being apart, thanks to Hera—it looks like Camp Jupiter is preparing for war. As Annabeth and her friends Jason, Piper, and Leo fly in on the Argo II, she can't blame the Roman demigods for thinking the ship is a Greek weapon. With its steaming bronze dragon figurehead, Leo's fantastical creation doesn't appear friendly. Annabeth hopes that the sight of their praetor Jason on deck will reassure the Romans that the visitors from Camp Half-Blood are coming in peace. And that's only one of her worries. In her pocket, Annabeth carries a gift from her mother that came with an unnerving command: Follow the Mark of Athena. Avenge me. Annabeth already feels weighed down by the prophecy that will send seven demigods on a quest to find—and close—the Doors of Death. What more does Athena want from her? Annabeth's biggest fear, though, is that Percy might have changed. What if he's now attached to Roman ways? Does he still need his old friends? As the daughter of the goddess of war and wisdom, Annabeth knows she was born to be a leader—but never again does she want to be without Seaweed Brain by her side Narrated by four different demigods, The Mark of Athena is an unforgettable journey across land and sea to Rome, where important discoveries, surprising sacrifices, and unspeakable horrors await. Climb aboard the Argo II, if you dare. . . .

Demigods Nico di Angelo and Will Solace must endure the terrors of Tartarus to rescue an old friend in this thrilling adventure co-written by New York Times #1 best-selling author Rick Riordan and award-winning author Mark Oshiro. As the son of Hades, Nico di Angelo has been through so much, from the premature deaths of his mother and sister, to being outed against his will, to losing his friend Jason during the trials of Apollo. But there is a ray of sunshine in his life–literally: his boyfriend, Will Solace, the son of Apollo. Together the two demigods can overcome any obstacle or foe. At least, that’s been the case so far... Now Nico is being plagued by a voice calling out to him from Tartarus, the lowest part of the Underworld. He thinks he knows who it is: a reformed Titan named Bob whom Percy and Annabeth had to leave behind when they escaped Hades’s realm. Nico’s dreams and Rachel Dare’s latest prophecy leave little doubt in Nico’s mind that Bob is in some kind of trouble. Nico has to go on this quest, whether Mr. D and Chiron like it or not. And of course Will insists on coming with. But can a being made of light survive in the darkest part of the world? and what does the prophecy mean that Nico will have to “leave something of equal value behind?” Nico will have to face demons both internal and external as his relationship with Will is tested to the core in this standalone adventure featuring two of the most popular characters in the Percy Jackson saga.

Percy Jackson, now a high school senior, needs three recommendation letters from the Greek gods in order to get into New Rome University. He earned his first one by retrieving Ganymede’s chalice. Now the goddess Hecate has offered Percy another “opportunity”—all he has to do is pet sit her mastiff, Hecuba, and her polecat, Gale, over Halloween week while she is away. Piece of cake, right? Percy, Annabeth, and Grover settle into Hecate’s seemingly endless mansion and start getting acquainted with the fussy, terrifying animals. The trio has been warned not to touch anything, but while Percy and Annabeth are out at school, Grover can’t resist drinking a strawberry-flavored potion in the laboratory. It turns him into a giant frenzied goat, and after he rampages through the house, damaging everything in sight, and passes out, Hecuba and Gale escape. Now the friends have to find Hecate’s pets and somehow restore the house, all before Hecate gets back on Saturday. It’s going to take luck, demigod wiles, and some old and new friends to hunt down the animals and set things right again.