APA (7th ed.) Citation

Christie, A. (1990). The secret adversary. Project Gutenberg.

Chicago Style (17th ed.) Citation

Christie, Agatha. The Secret Adversary. Champaign, Ill: Project Gutenberg, 1990.

MLA (9th ed.) Citation

Christie, Agatha. The Secret Adversary. Project Gutenberg, 1990.

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