His latest suspense novel, Nowhere, was published in 2007. Costello also wrote Island of the Skull (Pocket Books), an original prequel to Peter Jackson's film, King Kong.
Costello's work for children include the book series The Kids of Einstein Elementary, published by Scholastic, and Magic Everywhere (Random House), as well as games including Aladdin’s Mathquest (Disney), A Cartoon History of the Universe (Putnam) and two math games based on the hit PBS show Cyberchase. He is designer of role-playing and board games, including Dungeons & Dragons, Call of Cthulhu, Batman, Lone Wolf & Cub, and many others.
Recently, Costello worked on Rage, a post-apocalyptic action-adventure game for id Software and wrote its novelisation, as well as a new game for Eidos with Neil Richards and Swedish developer Avalanche.