Leareth doesn't resist. And he takes his shields down fully, this time.
He's been reading her thoughts this entire time - or, well, at least during the two blocks of time after he was sufficiently startled to do it instinctively and get around the compulsion against all volitional actions. (Leareth is almost two thousand years old and has spent a great deal of that time frequently in danger, and reflexes transfer between his incarnations much better than explicit memory. He has a lot of trained combat-magic reflexes instincts.)
Underlying all of his thoughts, his current attitude toward Carissa herself is one of - some sadness about the position she's been in, that has pushed and incentivized and constrained her into such a...small...shape. Confusion, at the entire way she reasons around goals and values; it's not just that it's alien, many pieces of it are actually less alien to Leareth's own thinking than how Heralds think about ethics, it's just - it doesn't entirely hold together. But there's also growing respect. For her obvious intelligence, and ambition, for the fact that she's clearly trying to grow, to become more...
She's pretty good at noticing her confusion and making inferences. To the extent that she hasn't made all the right inferences, with Leareth, it's because he's been deliberately concealing as much as he could get away with. And also, in addition there's the vast cultural gulf between their worlds, there's the fact that Leareth's existence would sound shocking and implausible to most Velgarth natives.
She's right to be confused about having captured him, of course. He would respect her reasoning a little less if she hadn't noticed it. The missing piece here is that it shouldn't have happened, in any sane world - Leareth's mind flashes briefly over all the absurd components that went just exactly wrong, the earthquake alone must have burned a vast quantity of Vkandis Sunlord's resources. And toward a goal that will probably harm Iftel in expectation, since Leareth has in fact revealed relevant strategic information to Chelish leadership already - and will end up giving them a lot more intelligence, if they successfully get him back to Cheliax.
The missing context is that Vkandis doesn't like Leareth. 'Doesn't like' is an understatement. He's set Leareth on fire twice for attempting to open communications with Him. None of the gods like Leareth, and he's not entirely sure why - due to the fact that They refuse to talk to him - but he has a few guesses. The gods of Velgarth don't care about the things Leareth does, which draw significantly on his understanding of what most mortals want for themselves; people value continued existence, lives that contain successes and joys and a minimum of pain. Certainly the endless grind of subsistence farming, with its occasional inevitable years of starvation, seems pointlessly bad to Leareth in the same way that the endless recycling of souls without memories does. And - it seems that the gods don't like change. That they oppose human progress almost on principle. At least, that's one of the simpler theories to explain the particular plans that tend to have gotten him murdered.
Leareth hadn't really wanted to reveal this much, so soon; at the very least, even in the worst-case scenario, where they hauled him back to Cheliax and threw every resource at interrogating him, he could at least have stalled. Maybe long enough for his people to intervene - if not in rescuing him, at least in mounting a counterattack.
Long enough for Vanyel to do something, maybe.
...Vanyel.
That feels - relevant, here, actually. Herald Vanyel. His destined enemy, according to the gods' Foresight. And yet, by some bizarre further meddling - one which Leareth is still confused about - they were granted the chance to speak. Over a decade of conversations in dreams. He's tried to teach Vanyel. To make him stronger, which on the face of it is bad for Leareth's goals, since he plans to invade Valdemar for the next stage of his fight against the gods.
Because all the methods of teaching someone to reason more clearly, to come to more true beliefs and take more effective actions toward their goals, are ones that make them stronger.
And Leareth believes that he's right. That's the core of stability behind all of his thoughts. It's the anchor holding the fear and exhaustion, the distracting thirst and headache, at bay. Leareth has spent a very, very long time trying to understand what would be best for the world - what would lead to the greatest flourishing for all the sentient, conscious beings...
He doesn't like the answer.
Carissa thinks that Leareth is Evil, according to her world's classification. Which, well, the Heralds of Valdemar would agree. The Heralds of Valdemar are very Lawful Good. (Except - maybe not Vanyel, maybe not anymore - because over those long years, Leareth has forced Vanyel to stare into just how broken, and how inconvenient, the reality they find themselves in is...)
Leareth is ruthless at achieving his goals. His goals...just happen to involve wanting the world to be less broken for everyone, for all the people, not just him.
- a tower against the stars - lights in the world, he says to Herald Vanyel in the snow - and it is too late to save all of them, it was always too late, but it is never too late to save some -
Leareth is willing to kill millions of people (though he hopes to get them back, afterward) in order to take his fight to the gods, because the world as it is now is unacceptable, and for thousands of years no one and nothing has changed it, and so if he doesn't act then probably things will never, every change...
He wonders what Vanyel is thinking right now.
It's an interesting test case, in a way - for whether Leareth is right, that he believes true things and therefore making his enemies stronger, showing them how to better understand the world, will in expectation lead to them no longer being his enemies.
If Vanyel, knowing about Cheliax, mounts a rescue attempt, then he'll know he was right.