They keep the book. It lives in Mione's room under a floorboard, and once a year somebody writes in the margin.
MalfoidNext shortest night I am bringing a better blanket and a bottle, and I am going to say something worse than last time.
MioneYou said you would give the name.
They do it again in December, and in March, and the room stops being a night and starts being a thing the three of them do, which the governors never find out.