APA (7th ed.) Citation

Bradley, M. H. (2007). The Fortieth Door. Project Gutenberg.

Chicago Style (17th ed.) Citation

Bradley, Mary Hastings. The Fortieth Door. Project Gutenberg, 2007.

MLA (9th ed.) Citation

Bradley, Mary Hastings. The Fortieth Door. Project Gutenberg, 2007.

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