Somebody was in your dreams last night. More precisely, somebody you couldn't identify was magically poking around inside your brain, while you were asleep and had all of your natural defenses about as low as they can normally get, and got front-row seats to events of your past life that you've told all of one person about - and then only briefly.
Aside from being disturbing as hell, this is potentially a Really Bad Thing. There's no telling what dangerous secrets that mostly-invisible dream-girl could have discovered while poking around your unguarded memories, or what she might have left behind. Fortunately, while there isn't much you can do about the former issue, you can at least run damage control on the latter.
A quick look around confirms that Briar is sacked out in her little futon. Waking her is the work of just a few finger-pokes, although the way she comes awake, grumbling about breaking that same finger, costs you a couple of minutes of apology before you can start explaining yourself. Once she's awake, however, your grumpy fairy companion has no trouble taking in what you're telling her.
You spend the next ten minutes with the tiny, magical equivalent of a penlight being shone in your eyes, while Briar works spells and asks you questions about your dream and what you saw in it.
"Okay," she says at last. "The good news is that I found the magical trace for the spell or power this girl was using to spy on your dreams. There was no real attempt made to hide it, so we're probably looking at somebody who's young, new to dreamwalking, and overconfident enough in her skill at it to be careless. The even better news is that with the trace as a reference, I was able to give you a very thorough scan for anything else this girl might have put in your head."
"And what did you find?"
"I found no compulsions, suggestions, manipulated memories, or booby traps," Briar says firmly. "There is, however, a mark on your aura - like one of those personalized glyphs sorcerers use to tag their stuff and mark their turf. Looks like whoever she is, she intends to be able to find you again."
You scowl at this. From a certain point of view, you've just been branded like a walking side of beef - possibly literally, depending on how your unknown visitor regards humans. Just as concerning is the fact that symbols of this nature can be detected by their creators over sometimes startling distances, which makes them natural target-points for all manner of magic. The girl could teleport straight to you right now, assuming she has that capability, and some other spells - like, for example, the one that lets her dreamwalk - could also home in on the symbol to find you.
Your first impulse is to get rid of the mark, but your second is to keep it, and set up a trap to see if you can catch your unwanted visitor. You struggle to decide which is the more appropriate answer.