Orbiting a planet, there is a moon.  On that moon, there is a castle.  In that castle, there is - well, a lot of things, many of which will become relevant shortly.  But for the moment, let's focus on a particular cell: it's stone, with one wall in metal bars and a door hanging slightly open, and it has a wood bench big enough to lie down on in one corner.  In that cell, there is - no one, for the moment.