What's the Name of That Book??? discussion

SPOILERS ahead.



In each book, at the beginning of each chapter, a phrase appears in a rectangle indicating that it will appear in that chapter.
In the first book, the group of friends is being trained, and at the end of the book, they manage to escape. However, before escaping, they discover that they were injected with something, though they don't quite know what it is.
In the second book, a couple of them are hiding in a cabin in a snowy area.
In a book that is neither the first nor the last, a couple of the group go to spy on a black-market sale where the substance they were supposedly injected with as children is being sold. The man buying it says something about how the substance will make him stronger, immortal, or something like that, and after injecting himself, he goes crazy, leaving the boys bewildered.
In the last book they discover that what they were injected with was an alien microorganism they found in a meteorite, and in this book they are also told that they found a method to remove them, although the first girl who underwent the treatment (who is not part of the group of friends) ended up in a wheelchair, although the girl tells them that it is likely that this will not happen to them.