The diaries start out with her being sent away to boarding school at an age of 12, barely more than four years ago. They are mysteriously well written, to the point that the reader will really start to understand and feel what the girl goes through.

If the investigators decide to check up on who this girl is, they will find that she does in fact exist. She is 16, apparantly healthy. Nothing about her seems abnormal, though if the setting is modern, she might be a goth.

If the diaries are casually studied, it might be noticed that the last entries in the last book is in fact dated in the future.

If read from the first entry and outwards, even if just skimmed, the reader will feel more and more compulsed to read on. After reading the first four or five volumes, which now leaves Nina at 14, the reader will begin to remember things about Ninas life that she did not write down. This will not, however, be apparent to him (or her) unless he for some reason decides to go back and reference something he read earlier. At this point, it seems that Nina is becoming increasingly interested in the occult. Also, for the reader to stop reading for a longer amount of time, a willpower roll at x4 must be done.

Starting with the entry of 7/5 in the seventh volume, retelling Ninas 15th birthday, the reader will actually start to experience everything Nina does, sight, sound and feelings, as if he was a passenger in her mind. While in his mind, each day of her life feels like a full day, actually experiencing it will only take about half an hour, in which he will be in a trancelike state, only occasionally flipping the pages of the diary. By the end of each day, as Nina falls asleep, he will come out of the trance. Strangely, there are some days and moments that are simply missing. Now, a willpower roll of x2 is required to take longer breaks in the reading, and the reader will occupy all his free time reading the books.

Finally, reaching the entry for the current day, the spell that Nina has cast over the books will be final. Unless the reader is able to make a willpower roll of x1/2 (or x1), he will find himself actually in Ninas body, in full control. This will not be immediately apparant to him, as he, believing himself still to be a passenger, will do whatever he would expect Nina to do (and knowing almost everything about her, he has a pretty good idea), but something will feel odd. The realisation will probably hit him when he wakes up, still as Nina, the next day (if the player does not try to actively do something un-Ninaish, give an idea roll).

Of course, Nina is in control of the readers body. The exchange of memories that the diaries did was two-way, and she knows reasonably much about the life of the body she now inhabits, though she will not get this knowledge until the actual change happens (so the realworld Nina, if the players ever visit her, will have no idea of who they are and so on).

The reason for the books being imbued with this magic power is simple. Nina, when she began being interested in the occult, managed to cast a spell that showed her her future - mere weeks from the day of the swap, she would be kidnapped, raped and killed.

Scared to death, she made a pact with [insert deity here, maybe good old Mr. Tep], and her diaries were infused with magic that would allow her to change body and mind with whoever read them, as he or she came to the entry of the current date in his/her life. This dark pact and her later dabblings in these areas are what is missing from the readers mind. The books were also enchanted to become almost impossible to stop reading. The books were then sent back in time, to be found by some unsuspecting meddlers, at the day where she went to meet her fate by the hands of the rapist.

Any entries after this will disappear as the swap happens. However, if the person now occupying Ninas body writes in the diary, it will start to appear in the other version. This, along with small quirks in the personality of the body Nina is in, might give hints towards what has happened to the other players.

As for what happens after that, it's up to whoever uses the idea. Maybe the players find a way to swap them back, maybe they never notice, or maybe they manage to save the new Nina from her fate.

Stats:
Date: 4 years ago - some weeks into the future
Language: English
Description: Handwritten, quite standard faux-leather diaries. The earlier ones have girlish motives, the latter are plain black.
San cost: Well, what is fitting for suddenly realising that you are no longer yourself, literally?
Cthulhu Mythos: 0
Study time: 1d6 weeks + approx two more weeks after starting to experience life as a passenger in Ninas mind
Spells: None