:Three to six candlemarks, I think, but - don't start panicking unless it's been more than eight. If it takes longer than a usual deep scan for some reason, I'll ask him to send a note explaining that: 

So they leave a note at the drop point naming Melody and suggesting he send someone to pick her up in a candlemark.

Leareth's reply confirms this, and a candlemark later someone (not him) Gates to the specified point to meet Melody. 

And then they can listen in. 

"Thank you for coming." The woman speaks in strongly accented Valdemaran and looks very foreign. "I want to ask you questions with truth magic, first. Do you have any intention or plan of harming Leareth..." 

Melody passes all the truth-magic screening questions, and consents to having her surface thoughts quickly skimmed. 

And then the woman Gates her elsewhere. 

"Leareth. Thank you for - agreeing to take this step, I know it's a big ask. I'm Melody, one of Valdemar's Mindhealers - you asked for someone who knew how to deep-scan a person without leaving a mess. I'm confident I can do that." 

"Nayoki agrees. Thank you for volunteering; I know that given your state of information, it was not without risk, though I will reiterate that you are safe here and it is not at all in my interests to harm you." A chuckle. "Nor try to slip compulsions past the Heralds, who I am certain will be checking." 

Melody laughs as well. "No, I know, that's what I said. ...Ready to get started?" 

"Yes." 

"...I do need your shields down." Pause. "Thank you." 

...

The rest of the process has a lot of long silences; Melody is mostly directly reading Leareth's thoughts, not asking him questions out loud, and it seems most of the conversation is happening in Mindspeech. She does occasionally make surprised or thoughtful noises. 

It takes about four candlemarks in total (Melody is very efficient and Leareth is being maximally cooperative). The Andalites get some warning of this, since Melody thanks Leareth for his time and he thanks her in turn. 

The woman from before says something about checking Leareth for 'messes', presumably does so, pronounces him clear of Melody having tried to do anything to his head, and, noticeably relieved, Gates Melody back to her starting point. 

From which they can go and get her.

Melody looks very tired, and also relieved. :Want the debrief on it now? I, er–: glance around, :I think given some - guesses of mine - we should talk without the Heralds present. Hmm. Maybe Mardic would be safe: 

<Once they check you for mind-magic, I think.> He is - confused, again, that she wouldn't want the Heralds present. He is tired of being so confused.

:–Right, of course. And I should have Gemma check me for, er, anything subtler. He's not a Mindhealer and we were alone for it, but Nayoki could theoretically have done something to my head that wouldn't show up to mage-sight: 

All three of the Herald-Mages check Melody for compulsions. Mardic, with his well-honed Othersenses, spends the longest, and confidently pronounces her clear. 

Melody nods, thanking him and absently patting his shoulder. :You could drop me off back in Haven and I can check on Van after Gemma clears me, and then come back to debrief properly? Er, I can give you the short version now if you want, though: 

<I could get the short version on the way to Haven, maybe.> Then it won't be conspicuous there are no Heralds wanted.

They leave the three Herald-Mages to guard the ship, and get on the shuttle. 

:He's not trying to trick you: Melody tells Matirin. :He's incredibly sincere about this alliance, and - how important it is to him, and he's willing to be very patient on the technology question - he thinks that even if it takes him a century of trust-building to get your species' help, it'll be a thousand times better than his alternatives. I...do have a better sense of what would prompt him to switch sides in the war, I think. He genuinely considers it unlikely he would do that, but he's confused and suspicious about the Yeerks' actions here, he's going to be looking for missing context: 

<Missing context for - why they started conquering worlds?>

:Why they turned on Seerow, and why they're so unwilling to come to any truce with the Andalites. To be clear, he thinks the balance of probability here is on your story being exactly what happened, just...he's noticing some confusion: 

<I think I'm having trouble picturing - why, even if we were wrong about that, it might prompt him to switch sides - to be clear I have no particular reason to suspect there's anything to the story more than what I have already explained, but - even if there were, Earth didn't start it. Even if there are a bunch of Andalites who also need to be arrested - I am confused about the person who'd give them Earth, in response.>

:He's holding mental space for a lot of unknown unknowns, here. If it were just the known unknowns - are the Yeerks as evil as you've described them, did they initiate hostilities, are the Andalites a lot worse than you've come across so far - then I think he'd be a lot readier to swear he won't change sides; he would only do it if, for some reason, Earth's leadership preferred the Yeerks to not, which seems rather unlikely. But he's coming into an alien war with almost no context. He doesn't want to rule out that he's wrong about some background assumption that he hasn't even thought of yet: