One of the InMe guidelines is "speak with any one human." Unfortunately, there's no spell I can find that uses that guideline, so I'm not entirely certain what it means. So, I came here to see if I could get any guidance.
The spell is InMe, which must tell us something.The Mentem part implies that the "speaking" we're talking about is mental. The Intellego part implies that you learn something from the target's mind. My best guess is that this guideline let's you speak mentally with the target of the spell. At the very least it implies that you can hear their communicative thoughts. But does it go both ways, i.e., can you send thoughts as well as receive them? My gut tells me yes, and I'll explain why.
First, the guideline says "speak," which implies two way communication.
Second, another level 15 guideline is "read a person's surface thoughts." But when you mentally speak with a person you don't detect all of their surface thoughts, just the ones that they want you to hear. So, if the "speaking" were just receiving thoughts, then it would be less effective than another guideline of the same level, which lets you read not only the surface thoughts the target wants you to read, but also the ones they don't want you to read.
Of course, since if you're sending thoughts as well as receiving them, I'd toss on a Creo requisite to the spell. I'd imagine that would be free requisite, since you couldn't send anything without the requisite.
In any case, here's a sample spell that I think meets the requirements of this guideline. But I'm not 100% sure and would welcome any thoughts people have as to what exactly it means to have an InMe guideline that allows you to "speak with any one human."
R: Arc, D: Conc, T: Ind
This spell allows the caster to communicate mentally with one person for whom he has an arcane connection.
(Base 15, +4 Arc, +1 Conc)
Of course, you'd be wise to use it only with someone that it was designed for because it's a high enough spell to cause warping. But if you designed it specifically for an important character (like a companion), it might be a very useful spell to have.
Which makes me think that an alternative would be:
R: Touch, D: Conc, T: Ind
This spell allows the caster to communicate mentally with one person whom he is touching.
(Base 15, +1 Touch, +1 Conc)
If this spell were mastered to allow it to be cast silently and without gestures, it would be useful in quietly consulting with someone in a way that couldn't be overheard. Better yet, it doesn't cause warping.