APA (7th ed.) Citation

Riordan, R. (2012). The Heroes of Olympus The Mark of Athena. Penguin Books Ltd.

Chicago Style (17th ed.) Citation

Riordan, Rick. The Heroes of Olympus The Mark of Athena. Penguin Books Ltd, 2012.

MLA (8th ed.) Citation

Riordan, Rick. The Heroes of Olympus The Mark of Athena. Penguin Books Ltd, 2012.

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