"Mark of Athena" is the third book in the Heroes of Olympus series by Rick Riordan. It follows the adventures of demigods Percy Jackson, Annabeth Chase, and their friends as they embark on a quest to retrieve the Mark of Athena, a powerful artifact linked to the goddess Athena. The story is set in a world where Greek and Roman mythology intertwine, and the characters must navigate various challenges and monsters. The narrative focuses on themes of friendship, bravery, and the struggle between good and evil. As the demigods journey through ancient sites and face formidable foes, they learn about their heritage and the importance of unity. The book combines action, humor, and mythology, appealing to young readers and fans of fantasy literature.