APA (7th ed.) Citation

Riordan, R. (2012). Heroes of Olympus: The Mark of Athena. Puffin Books.

Chicago Style (17th ed.) Citation

Riordan, Rick. Heroes of Olympus: The Mark of Athena. London: Puffin Books, 2012.

MLA (9th ed.) Citation

Riordan, Rick. Heroes of Olympus: The Mark of Athena. Puffin Books, 2012.

Warning: These citations may not always be 100% accurate.