APA (7th ed.) Citation

Christie, A. (1998). Secret adversary by Agatha Christie. Project Gutenberg Literary Archive Foundation.

Chicago Style (17th ed.) Citation

Christie, Agatha. Secret Adversary by Agatha Christie. Salt Lake City: Project Gutenberg Literary Archive Foundation, 1998.

MLA (9th ed.) Citation

Christie, Agatha. Secret Adversary by Agatha Christie. Project Gutenberg Literary Archive Foundation, 1998.

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