New York Times #1 best-selling authors Rick Riordan and Mark Oshiro collaborate again on a new adventure in which Nico di Angelo teams up with his half-sister Hazel Levesque to protect . . . monsters?Nico di Angelo is feeling antsy. It's been almost three months since he and his boyfriend, Will Solace, returned to Camp Half-Blood from their journey to Tartarus, and there hasn't been a demigod quest or a conflict with monsters in all that time. So, when Nico's half-sister, Hazel Levesque, asks him and Will to join her at Camp Jupiter on the West Coast, he shadow-jumps at the chance to get away and do something.In her Iris-message, Hazel had said that she needed the boys' help with an "issue" with some "new guests." What she didn't say was that she's providing a haven for a group of monsters who escaped the Underworld! Apparently, the self-proclaimed "mythics" learned from Nico and Will themselves that they have options and don't have to be evil. But their integration into the Roman demigod camp isn't exactly going smoothly.As Nico and Will endeavor to build bridges between the refugees and the demigod campers, the mythics start disappearing from camp, one by one. A mysterious dark force is at work, and its plan is to punish all monsters for their past crimes. Things only get worse when Hazel learns that she is closely connected to that force . . .In this brilliantly inventive and laugh-filled adventure, the best-selling team of Rick Riordan and Mark Oshiro manipulate the Mist to make readers see things in a whole new light.