APA (7th ed.) Citation

Simkins, M., Mortimer, R., & Mortimer, C. (2015). Dear Lupin. Nick Hern Books.

Chicago Style (17th ed.) Citation

Simkins, Michael, Roger Mortimer, and Charlie Mortimer. Dear Lupin. London: Nick Hern Books, 2015.

MLA (9th ed.) Citation

Simkins, Michael, et al. Dear Lupin. Nick Hern Books, 2015.