APA (7th ed.) Citation

Horowitz, A. (1999). The Unholy grail: A tale of groosham grange. Walker Books.

Chicago Style (17th ed.) Citation

Horowitz, Anthony. The Unholy Grail: A Tale of Groosham Grange. London: Walker Books, 1999.

MLA (9th ed.) Citation

Horowitz, Anthony. The Unholy Grail: A Tale of Groosham Grange. Walker Books, 1999.

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