MYSTERIOUS PLACES is specifically a collection of (mysterious) locales, each of which is presented with a history, associated characters, at least one plot device, different possible reasons for the player characters to become involved, and potential resolutions to the problems that the location poses. There is also information on how to adapt the setting to other types of territory: how to run a particular scenario in a downtown location rather than a rustic village, for example. The mystery is really what drives the plot for each location, so a lot of investigation is called for (in this case, the "guns" from the above quote are metaphorical). I believe the writeup for each location has enough depth to sustain a dedicated group poking at shadows without the Storyteller needing much prep ahead of time. It's not written in a story-line format, such that the investigators must do A to get to B to accomplish C; however, one could reasonably sit down, open the book, and play a few sessions straight from the chapter, provided the ST is familiar with the material from that section and limits the amount of outside influence in the story. It seems that MYSTERIOUS PLACES has this in mind, since each of the locations is designed to emphasize isolation.