At first because him capturing you would be a very bad thing on several levels even without you knowing my name. More recently because he's near enough to the steppes to be threatening. And now that you've mentioned it, army of sorcerers."
"We could even go to Fairyland and make a gate from there to the other side of this planet, then to Thorn's court from there. Then anyone who comes through is definitely not getting to us. Can't say the same for whoever lives there, though."
"Well, yes, but I want to avoid Thorn's people rampaging here as much as you do. Would he be deterred by the gate going to somewhere buried deep underground? To a deserted and distinctly uncomfortable wasteland? To somewhere it could plausibly have been directed from on purpose, with people to conquer if he wants, but that won't lead him to us?"
"I can't claim to really understand his motives beyond that he collects sorcerers, he's very good at it, and he's more than sadistic enough that staying here with you transmuting metals all day is idyllic by comparison to what I'm looking at if he takes me back again."
We can just put the gate in one of those hidden rooms that take Allomancy to open. If anyone other than me comes through, it might not stop them for long but you'll have a chance to run for it and come back in three hundred years."
"I can't get very far running on a 'take no new action' to which you've been adding as-needed exceptions."
"I'm going to edit it of course. Something much broader, about saving the world and not overthrowing me. Once I work out how best to phrase it."
"I wasn't overthrowing you or endangering the world before," she points out.
"You weren't endangering the world. You were giving me orders and taking issue with how I run my empire, and that's a combination that I plan to avoid."
"If I don't go after Thorn directly then he'd be adjacent to the likely future human colony, and he doesn't sound like a good neighbor to have. Unless this is a really terrible idea in some way I don't know about, it seems like an obvious decision to me."
"That makes this higher stakes and more important. But he shouldn't get a chance to give me loophole-less orders, and he surely won't expect any of this kind of magic."
As it is, let's go get started. Follow me."
He heads downstairs.
She follows. Of course. "I don't have much to argue with, if Thorn being preposterously dangerous won't cut it. You could send me to find someplace farther from him than the Steppes."
Is there such a place? That would be strictly better. but from what you said earlier there aren't a lot of places uninhabited enough."
"It's not a good sign. He barely had me do anything for him because he likes a certain amount of psychological brokenness in his vassals before he lets them take any substantial actions, that he couldn't get me to quick enough to suit him, which is why he sold me; I don't know what defenses he has but he collects sorcerers. I don't know a place better than the Steppes but I could look."
"How good are Fairyland's maps? If I tell you to come back in a few days with the best place to put a human colony, would you be likely to find a better suggestion? Thorn can be dealt with later."
"There are maps; they aren't very high-resolution. A few days wouldn't be long enough because the existing gate isn't near a library and I can't guarantee that a new gate made to a library would settle quickly."
"It could take more than days? We really were lucky last time around."
They reach the room where the chrome and cadmium came from. He opens the door with Allomancy, audibly moving the bar that locks it. "If you put one end of the gate here, you'll at least have warning if anyone who isn't me comes through."