Sinmore will head to the dock where he often fished and inform Sanno (if he doesn't already know) to look for a pool on the west side of the waters, those were some of his favorite places. Basically looking for clues. Sinmore probably can't find that pool as easily as Sanno can.
Rhodri suggests going back to the covenant for a place of safety, but that depends on how much the trip tires Sanno. He is not against accepting the hospitality offered here, though.
As a reminder, Maribus disappeared when he came here because he thought there was information that would cause trouble for Leona, and he wanted to cover it up before anyone found it. He did not disappear on a fishing trip.
It took from dawn until early evening to get here; if you left now you would get to the covenant a little before dawn. (The trip up the river didn't take long, but you also trekked overland for about four hours.)
Detective work is still an early science 
. Sinmore is just trying to follow in his footsteps a bit, he wrote so much about this place, and see if that gives her any ideas. Once his favorite spots are searched we should look around this area more thoroughly.
The next morning, you investigate Maribus' favourite fishing spot on the dock (unless anyone else objects). Sanno catches a lot of trout. Sanno checks the other fishing spot, and finds it mostly dry, since the trout avoid the deep pool in the winter (and remember, your boat is back at the river dee; you had to leave it behind to travel overland to lake vyrnwy). How long will you spend letting Sanno fish?
Sinmore isn't about to let the poor guy go hungry. She'll wait til he's ready, but if after it seems he should likely be full she'll ask about his progress and any findings and remind him they have other places to check.
Sanno has the personality trait of Glutton at +3. The rest of you are likely to pick up on that pretty quickly as he tears into live trout. He will sit and eat fish for as long as he's allowed.
What do folks want to investigate the next morning when they get tired of watching Sanno eat?
Sinmore will venture down the trails that a traveller likely takes to get to this place, straying off the path here and there and casting spontaneous Rego Corpus spells to make human items float in the air (her Intelligo stinks, but if she draws a big circle she can float things in the circle she can't see). She's looking for perhaps a sign of foul play, a body, blood, body parts, etc.
As folks are wandering about aimlessly, a flash of fire catches Iapetus's eye. He squints to look out toward the water, and notices faint licks of flame just barely perceptible through the fog on the lake. As his eyes strain to see better, he realizes that the fog in that spot is much thicker there than it is elsewhere. Fog and flame on an island in a lake... All four elements bound in one place.
Regardless of whether the spell works the way she expects it will, Sinmore begins drawing circles and sponting Rego Corpus spells. The first casting does nothing. The second casting botches, (no Twilight), backfiring in such a way that Sinmore is forced onto her knees, and her arms involuntarily rise up in supplication towards the sky. That's when she realizes, this aura feels really weird.
Sinmore's master William had often remarked as she struggled with her lessons on Magic Theory, that he was safe from apprentice-pilfering Bonisagus magi. Sinmore remembers this as her arms raise beyond her control until she breaks the circle with her foot and looks around, hoping no one saw her. Getting back to her feet she is dusting off her clothes when she feels like the spell is still affecting her. Taking another moment she realizes it's not the spell but the aura.
"What in Surtur's name?" she says to herself and begins quickly making it back to the lands around the water and the tower. "Hello? Is anyone else feeling that?" she calls out to the others that travelled here with her.
((Can she give a name or a description to how the aura feels? Has she perhaps encountered it before?))
If Iapetus noticed Sinmore's strange action, he was polite enough to look away. The Spaniard is, in fact, staring through the mists over the water, one hand on the wrapped handle of his mace, the other tucked into his broad belt. He doesn't respond to Sinmore, but mutters softly to himself in Spanish. "Flames of the earth, crash of the waves. Mist and smoke, dust and wind. Thunderstorms on the burning mountains. Ahhh.. where's a mermaid when you need one?" Shaking off whatever odd trance he was in, Iapetus turns to Sinmore with an faint smile, then addresses the group as a whole. "There is an island in the mists, and the fog is thicker there, unnaturally so." He has returned to Latin again. "Someone has put a flame on the island, and the whole thing is well-coated with things not natural. I rather like it. Perhaps we should investigate?" He stretches, the long ilde having made the Tytalus restless, a joint in his back making a creak and pop as he stretches it out. Iapetus strides over towards the water for a better look, not that it will improve much by the ten feet he's moving.
She's never experienced anything like it. It doesn't feel wrong like being in a hostile aura does, but neither does it feel right like being in a proper Magic aura, either.
His view from the shore is not significantly better than his view from whence he first noticed it 
Care to get closer?
Sinmore joins Iaeptus by the water and peers into the fog. "Sanno!" she bellows. "Sanno come here please, we may have found something!"
"I cannot swim, so if we're heading to the island we'll need a boat and our pilot."
Sanno emerges from the lake and bounds up to Attravere. "What's up, 'Trav?" he pipes. When he realizes Sinmore did not summon him on his magus' behalf, he looks deeply offended, and slinks back under the lake's surface.
"What?! No wait you little...Sanno we found something, come back up! This might be what we're looking for!" Sinmore calls after the otter. "Attravere, explain it to him would you? This is for Maribus."
I believe you cannot affect a Target you can't perceive, but you can affect a target you can't perceive. For example, a T: Room spell affects everything/everyone inside whether you can sense them or not, but you have to be able to sense the room.
I think that spell would be T: Hearing, not R: Voice.