Be an Interplanetary Spy

Aimed at younger readers, these books were published only in paperback form, with brightly coloured covers and were heavily illustrated in black and white. Unlike other interactive novel series such as Choose Your Own Adventure stories or Fighting Fantasy gamebooks, each Interplanetary Spy book is comprised largely of illustrations in a style that mixes comic book-like line drawings with blocky, straight edge illustrations matching the graphical quality of video games from the time of publication. Rather than requiring readers to select from various actions and directions, or succeed in dice-driven 'combat' to progress through the story, these novels mostly involve puzzle solving. Image-based challenges such as mazes, pattern matching, and visualization problems are common throughout the series, with all stories being presented in second-person point of view. The writers frequently used the books' own ISBN numbers, which they called "Interplanetary Spy Binary Numbers," as codes or clues within the stories.

By including blank spaces or boxes for writing, puzzles that required pages to be folded over and even a cutout model in one novel (The Star Crystal) the reader was actively encouraged to make changes to the books themselves. Because of this, it is almost impossible to find a copy today in mint condition.

The underlying concept of the series is that the reader is a member of an agency known as Spy Center, an organisation that maintains order throughout the galaxy and falls partway between a police service and an intelligence agency. This agency has its headquarters in Sector 666, known as 'The Sector of Illusions'. The reader's character is usually referred to simply as Spy, and the story and illustrations almost always deliberately avoid identifying the Spy's gender or any specific physical characteristics, ensuring the widest possible chance of affinity between the Spy as character and the reader. Individual stories are stand-alone and need not be read in any particular order to succeed, however several characters recur throughout the series and earlier events are often referenced later.

Each novel presents an encapsulated crime or mystery to be solved, and the overall series charts the reader's progress up the ranks with a number of promotions being received over the entire run of novels. Most novels follow the basic format of the reader being contacted by Spy Center who then assign them a mission and usually issue them with an associated disguise. There are often people that the reader must contact, usually spies themselves or else working in league with Spy Center.

The stories are quite linear, with the reader advancing through the set plot by solving a number of puzzles of a 'succeed or fail' style, said failure often resulting in the Spy's death or the story otherwise immediately coming to an end. As such, the reader's choices rarely impact the storyline itself, only their progression through it.

Note that while there are "Story by" credits for the series, writers designed the puzzles as well, sketching out the designs for the illustrators, who then rendered them in the distinctive, comic book style of the series. The twelve books, published in timeline order, are:

• Gamebook
• Interactive Fiction
• Choose Your Own Adventure
• Fighting Fantasy
• Time Machine (novel series)
• Visual Novel