The Nico di Angelo Adventures

By Rick Riordan

These co-written novels follow Nico di Angelo and Will Solace after their journeys with Percy Jackson and the other demigods. Start with The Sun and the Star, written by Rick Riordan and Mark Oshiro, then continue with The Court of the Dead. They extend the Riordanverse and assume familiarity with The Heroes of Olympus and Trials of Apollo.