APA (7th ed.) Citation

Twain, M. (2004). A Double Barrelled Detective Story. Project Gutenberg.

Chicago Style (17th ed.) Citation

Twain, Mark. A Double Barrelled Detective Story. Project Gutenberg, 2004.

MLA (9th ed.) Citation

Twain, Mark. A Double Barrelled Detective Story. Project Gutenberg, 2004.

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