From the World of Percy Jackson: The Court of the Dead: A Nico di Angelo Adventure

Rick Riordan and Mark Oshiro collaborate on a new adventure featuring Nico di Angelo. After three months of quiet at Camp Half-Blood, Nico accepts an invitation from his half-sister Hazel Levesque to visit Camp Jupiter on the West Coast. Hazel's Iris-message mentions she needs help with "new guests," but Nico and his boyfriend Will Solace discover she is harboring monsters who escaped the Underworld. These creatures, calling themselves "mythics," have learned they don't have to be evil and are attempting to integrate into the Roman demigod camp. As Nico and Will work to build understanding between the refugees and campers, the mythics begin disappearing one by one. A mysterious dark force emerges, intent on punishing monsters for their past crimes. The situation becomes more complicated when Hazel realizes she has a close connection to this force. The story follows the team's efforts to address the crisis while navigating the challenges of coexistence between two very different groups.