Originally created for 7- to 14-year-olds, the books are written in the second person. The protagonist—that is, the reader—takes on a role relevant to the adventure, such as a private investigator, mountain climber, race car driver, doctor, or spy. Certain books in the series allow readers choice of who to take the role of, for example, in an adventure book, readers may be prompted to choose between a climber, a hiker, or a traveler. Stories are generally gender- and race-neutral, though in some cases, particularly in illustrations, there is the presumption of a male reader (the target demographic group). In some stories, the protagonist is implied to be a child, whereas in other stories, they are an adult.