This prologue is a continuation of sorts of Midnight Tides.
At the end of that book, Trull Sengar decides to stay behind in the Letharii capital city to try to be a moderating influence with and towards his monstrous brother, the Empoeror Rhulad.
Apparently that did not work out very well, as Trull is now being given the ultimate punishment of his people, a permanent expulsion, with a permanent expungement of his very memory on top of it. not for acting against Rhulad - but simply for questioning him and his mysterious godly sponsor.
Late in the book Rhulad had mentioned opening gates to cause the oceans and rivers of some worlds to floow others so that the Edur can travel between worlds in ships.
The place they are improsoning and punishing Trull sounds like just such a world. He is scarred - with ash driven into the wounds in a form of primitve tatooing. And he is made to be forever bald. And then he is left behind in chains.
Trull has just discovered how much of a monster his brother really has become. Tyranny sucks.
