He found Kralin largely by accident.
His progress was slow, now, slower even than his earlier stalk; he had much less idea of which way to go, and spent more time looking in side chambers. That was how he noticed what seemed to be an eating area; the storeroom was closed tight, with a pair of human guards watching it from across the room, weapons ready at hand.
They weren’t watching very closely. If they had, they might have noticed that the chains slung across it were weak; some of the links had been repeatedly heated and quick-frozen. The lamplight helped obscure the sullen glow of the metal when it was hot; the ever-present rumble of stone probably obscured any minor cracking noise the metal made as it shifted.
The temper of the iron was quite thoroughly ruined. If he hadn’t spent so much time attuned to stone, feeling his way around the lowest caverns, he wouldn’t have noticed it, but in those moments he could sense the flaws even in the worked metal. A good hard shove, with the weight of the door and a body behind it, could snap them.
Kralin was there, all right, and obviously not too unhealthy. Mulin gripped his knife. He could speed his twin’s release, take down the guards –
But he forbore. If the guards died, the one controlling them would know that someone was there, and there were only a few people it could be.