"They have magic that blocks portals. I usually should be able to teleport across countries, to different kingdoms. I can't go outside of their containment." Istredd has never been so grounded since he first learned how to portal. He has tried too, he tested the boundaries out of curiosity, and he doesn't know how exactly they do it. Outside of the fact this is their world and they have more control over it than he ever will.

"It's the same in Free Cities, all the governments control what portals are allowed and to where." So it really is not specific to Thorne in this case. He doesn't know how it works in Free Cities, if they are blocked from it or not, but he assumes so. It makes a type of sense; in an atmosphere like theirs, with tension everywhere, they can't just have everyone porting around, skirting rules or politics.

"Nocwich can't allow any of us to go through the wrong portal either. If people could escape that way, they would have already." Not Istredd, but he certainly would have encouraged some of the others. Yennefer wants to stay there, and as long as she is there, so is he. "You can't walk over borders either. We can't leave. They barely let us leave the castle."