Publishers are increasingly creating real-life versions of “in-world” books as stand-alone titles or, more commonly, as part of broader licensing deals related to the TV show, film, or videogame in which the fictional versions of the books appear.

Insight Editions’ September’s Notebook, released this spring, is a prime example. The book, licensed by Warner Bros. Consumer Products, brings to life a journal kept by September, a pivotal character in the fifth and final season of Fringe. The title serves as the series’ comprehensive companion book, but with the added dimension of replicating a key item from the world of the show. In the series, the notebook—whose existence is revealed in the penultimate episode—contains all of the character’s observations, thus explaining the show’s complicated paranormal mythology.

“Our style is to work closely with the creators of the show, so we always look for these kinds of opportunities,” says Raoul Goff, Insight Editions’ CEO. “It was always our intention to create a book that was more than an outside-looking-in book. It serves a purpose besides just rehashing the shows.”

Insight did not know that the book itself would be featured in the show until late in the development process. The publisher was in the thick of creating the book even as the series finale was being written. Once it became known that the book would be included as a plot point at the end of the show’s run, Insight created the cover with that in mind and the production crew ended up using the actual book as a prop.

“It’s an intricate and sophisticated design,” Goff says. The cover is written in a font created especially for a fictional language used on the show. “They developed a whole language and font that the fans love to decode. That language is running through the book, and there are other Easter eggs for the real fans.” A removable belly band features the book’s title and a detailed description of the shrink-wrapped book’s contents and role in the show; when the purchaser takes that off, the book is revealed as an exact replica of what appeared on the episode.

The book was released in March, two months after the show’s January conclusion, followed by a deluxe collector’s edition at the end of May. The 15,000-copy first run of the trade edition, much of which was ordered pre-pub, nearly sold out at $50.

Insight Editions has published other in-world books, including The Dark Knight Manual for Warner Bros.’ most recent Batman feature film, and The Book of Cain, an in-world book from Blizzard Entertainment’s Diablo franchise.

Other recent examples of in-world books made real include Penguin’s Enchrydion from the animated Cartoon Network series Adventure Time, part of a broader licensing program; Little, Brown’s My Little Pony: The Elements of Harmony, a guidebook licensed by Hasbro with an in-world cover; the Poppy imprint’s William McKinley High School Yearbook, from the Fox series Glee; Hyperion’s novels tied to ABC’s Castle, which are “written” by the lead character in the series, a crime-solving mystery author; and B&H Kids’ Firebird, a picture book that plays a central role in the inspirational film Unconditional, which is about a children’s book writer/illustrator.