Kasirga 
Unbelievable...
The winds pick up again, and her body dissolves some more.
If you want to do something, do it now, else, we close this scene and move on.
Cidito answers, his tone quite serious, for once.
Things are that dire? I've got your back, pal, I'll do as fast as I can. Be careful in the meantime
As quick as you can old chum. The genie just dissolved. I want to cast Aegis of the Hearth on the whole island before she can return.
Ok. At some point, Cidito will teleport to you (using his AC to roberto) and crap a few twigs to serve as AC for the magi.
With Kasirga apparently gone, the clouds slowly dissipate, letting in rays of light.
One by one, the villagers slowly come out of the huts in which they had taken refuge, cheering Roberto.
ouch
Roberto nods in gratitude to Cidito. Just in the nick of time. This is my plan. I am going to cast Aegis of the Hearth around the village and their essential resources. Maybe even the whole island. The idea is to force the spirit to negotiate. Is anyone else coming to help? I will give it an hour before I start.
Roberto then smiles and waves his hands in a calming gesture.
Becalmed, good people. There is no danger at the moment, but we must prepare. I will need to speak with your leaders and elders. What is known about this woman and her claims on the land? What is the story of the situation?
The wonders of autocorrect, I guess 
Thanks for the laugh
(Lots of work, and it shows, sorry for the delay)
After a while..
Okay, pal, I've been running everywhere. Things are complicated.
I couldn't find the witch, but her servant girl told me she would be available in a few hours. Some other magi are willing, but they can't teleport. Looks like the witch can bring them, but there's warping involved. What do we do?
The people calm down a little at roberto's words, although there's still a lot of conversation and joy around.
But at Roberto's sollicitation, the hunched elder comes forward again.
We know nothing about this. She came here with the storm, and asked what we were doing on her island.
When I told her we held it but for the grace of King Triton, she flew into a rage, calling him a... what did she say?
A white-haired, wrinkled woman whispers into his left ear
Ah, yes, a, pardon my word, "lying backstabbing honorless traitor".
We asked her to wait until we could get word from our friends under the sea, which she agreed to. She then disappeared, but the storm remained.
Then... Some youth saw her speaking with merfolks from afar, and it didn't seem to go well.
She then came again to see us, and she was quite angry.
She said that King Triton no longer held any right to this island, that he had wronged her, and asked that we leave. To be fair, she was angry at our folks, not to us.
But this is our home, it has been for generations. My father's grave is here, and his father's too.
That's when Riad confronted her, but she broke his sword and wounded him greviously.
It was very stressfull. She kept coming and going, without warning, and she was so frightening! Always raging against Triton, asking us to leave... She never hurt anyone besides Riad, but she dispatched him to easily!
And... I'm confused, it's been so many things, and it's too much. We are a peaceful people, but this!
We feared we were left alone, and then, our folks, they told us that they'd send an ambassador to discuss with her, and it pacified her somewhat. And then you came, and banished her, for which we'll be eternally grateful.
Does this helps?
Roberto checks the time, trying to estimate how long it is until the sun sets.
Int +1, Artes Liberales 1, and then
Roberto checks the time: 1D10 = [10] = 10
botch check: 1D10 = [7] = 7
so he gets it wrong, but no botch.
The goal is to plan his casting of Aegis for an hour before sunset. He knows it at 20th level, and will take an hour to cast. Having failed his time check, he either thinks there is not enough time to wait (even if there is), or he cuts it too close to the line and will not finish until after sunset (which may be to late if the genie returns by then).
Then he listes to the elder...
contemplates...
Take me to Riad so that I may tend to his injury.
Too close to the line it is.
Headache + work, being terse.
The old man bows, as much as he can, before roberto.
You honor us by your kindness, esteemed one. Having such a mighty sorcerer take heed of our plights is more than we can ever repay. Please, follow me
He guides roberto through the village, which is in disarray due to the winds, but not seriously damaged, to a hut that's newer than those around it.
Inside, riad, lying on straw, feverish, a young woman by his side, looking at him with worry. She stands up when roberto enters
Roberto is mentally berating himself for his lack of thinking. He should have had Cidito bring Corpus vis. Yet still, he knows of a spell that will be helpful.
CrCo20 Purification of the Festering Wound: CT +16, Mastery 1 (Stalwart)
healing Riyad: 1D10 = [4] = 4
Successfully cast.
But by then he notices the sun getting low.
¡¡¡Triple-hijueputa!!!
Cidito! Meet me on the edge of the village! We need to start casting this Aegis now!
Roerto then craps a few twigs to use at Aegis tokens 
Roberto incants while the villagers look at him in wonder.
When he crounches to touch Riad's wounds, he feels the power flow from him to the young man.
In moments, riad's breathing eases, and he falls into sleep.
Thank you! Thank you, my lord! says the young woman. This is when Roberto notices her light pregnancy.
Wait, boss! I'm all alone yet, but the old one should be here soon!
(Gaah!! Okay, but just hurry up!)
Roberto turns to the expectant mother
Mother Mary and Jesus bless your family, and may your child grow hale and strong. Now if you will excuse me, I have a village to save!
When roberto reaches the townplace, Cidito is waiting for him, alone. Has Roberto been let down again?
Don't worry, boss. The witch had me drop some spider here. Said she'd come soon if it was okay
After a few moments, Roberto notices a wooden spider clambering back to the place, and then, a red light appears out of nowhere, expands quickly into a cocoon, which unwraps itself, revealing the Arcachne.
Roberto. I am alone, but here I am. Cidito said you were in dire straits. What assails you, that you'd need Andorra's entire cadre of magi?
I don't need everyone. Just the smartest one!
Madame Pontifex, I thank you.
I'm...
I am not sure what I am up against. A powerful genie, faerie, elemental, I don't know what. But it is a threat to the people on this island.
This started as a test, I was sent here to judge a case concerning this beings ancient claim on the land. A claim for which it refused to demonstrate evidence for and declined to discuss or negotiate. The spirit departed, and said it would soon return.
I may be screwing up this "test", but the sanctity of human life is paramount. These people think me a hero, and I world rather forefit my life than abandon them.
I personally know how to cast the classic Ritual spell, Aegis of the Hearth. Onlt at the fourth magnitude, so it might not be enough to ward it from enetring. But if it can be cast with enough Penetration force, it will greatly weakin it.
I do not wish to harm it if I do not have to. I only seek to convince it to negotiate.
I had a half baked idea. It seems to desire isolation. What if we set it up on Sa Dragonera? That uninhabitable rock part where we get the vis from. We could mage it a guardian of sorts. Strike a bargain. If it is a genie, a clever bargain may be the trick that would serve everyone's interest.
Win-Win 
A faint smile at the corner of her mouth
Aaaah, Roberto. Always the champion, often in trouble. I must say, you are a better person than I am.
She turns to her right
Blessed ancestor, if I may? I need you to keep out for us. Thank you very much.
Turning back towards Roberto
Okay. Correct me if I'm mistaken.
She paces around while talking, hands joined.
We don't know the opponent's exact nature, methods or abilities. This makes it quite difficult to defend against, which is complicated by the fact that it could strike at any moment, although it has expressed the desire to return soon.
This is were you screwed up first. Before antagonizing it, you should have tried to learn as much as you can about it. For all we know, it might be all lights and shadows, with little true power.
Nonetheless, if it is aggressive enough for you to expect imminent conflict with it, you should have struck first, and hard, while you could. This was your third mistake.
So now, we play catchup. Still, given your objective and lack of knowledge, your assessment looks to be right.
Sadly, I'm of no use there, and it is a grave mistake I'll need to rectify soon: I have never learned how to cast Day of Communion. So even if it's might is under the fourth magnitude, we won't have enough penetration to bar it. Still, if it stays outside, it should protect this village somewhat
Still, there's the other option: we relocate these people in haste. This is something I'm not looking forward, but if these people's life is important to you, this may be our best solution.
From then, you can face it, and try to struck a bargain. Your Sa Dragonera idea is a long shot, but if it worked, this would be to our advantage.
Sigh... I've spent the whole day enchanting, this is not what I want to do just now. You owe me. Yet, this may be worth it, so if you require my assistance, I may stay a little.
However, given what you say about your previous exchange with this creature, I have some reservations about your ability to get through to it. So if this fails, what do you do?
Oh, and, by the way, free advice: This attitude is your greatest charm and your greatest weakness. This may work on me, but don't assume it'll be the same for everyone.
(Wow, I had forgotten how verbose and pontificating she could be Sorry for the attitude!)
I did nothing to antagonize it. They are just oversensitive and easily offended, and seem to have an ambiguous sense of honor.
And I shall not ever be one who offers premptive violence. Combat is the final resort tool of diplomacy. The option must be on the table, but held in reserve until absolutely needed.
That is an unacceptable option. These people are of this soil. This is their life and blood.
I can cast an Aegis on my own. If you could watch my back as I do so, I shall circumscribe the settlement. The genie will be forced to meet me on the shore or be weakened by it.
I am going to play a hunch. Either the genie is too weak to face me and knows it, or is likewise hesitant to use violence and hoped intimidation would suffice.
One way or the other, I am going to take a chance.
Arachné rolls her eyes and raises her hands ¯\ /¯
Yet, she also has a friendly/amused smirk on her face, as if she isn't that surprised by this reply
And here I am, having foolishly offered my assistance. Well, you would have been an even greater fool not to take it.
...
Given the lack of information, and the fact that it could strike at any moment, my capacities are severely diminished. I am no flambeau, able to face anything at a moment's notice.
So I'll watch your back.
But I can't promise to be very effective, nor am I willing to suffer needlessly for whatever mess you find yourself into. I will try to stall it, and to protect you, but I won't put my life on the line, including incurring the enduring enmity of whatever that thing is, especially if I happen to disagree with your behaviour.
Is that okay?
If that's okay for Roberto, well, listing for reference:
Stressful (Kasirga could come at any moment, so she's not that relaxed), but not by much (only 1 botch dice), lvl 1 faerie aura. Hum... Given her mastery and all, that means at worst failure.
Note, she has no simple terram ward.
@Marko: Spells being specialized, I am of the opinion that a ward against metal doesn't protect against gemstone, nor against stone or earth. This is, in part, a deliberate choice, since it means it's harder to get warded against everything (takes a few years instead of 1-2), which, IMO, is a good thing from a GM and a player's pow. If you disagree, please let me know before I waste a season on this
"The DM is the game"
Diplomacy is important, but the point is that whomever is running a story/session should be free to interpret rules as they feel proper.
"The DM is the final arbiter of the rules."
I quote Gygax a lot
ReVi20r Aegis of the Hearth: Mastery 1 (Secure)
I don't remember what Secure means. I think a reduction in Botch dice?
Sta +1, Rego 10, Vim 5, Mastery 1, for a Casting Score of +17
Then three Fatigue Levels from Life Boost for another 15 points, running total of +32.
(He has Endurance of the Berserkers running in the Familiar bond)
then a die roll....
Aegis of the Hearth: 1D10 = [7] = 7
Casting Total of 39
add two points of Confidence to bring that up to 45
minus level 20, plus Penetration 2, equals a Penetration total of 27
Roberto circles the village's boundary, with Arachne walking a few paces behind him, using her staff to lean on, very much the image of the frail old woman.
It takes time enough, but the ritual is completed without interruption.
Well done. I didn't knew you could cast an aegis on your own. Color me impressed.
Now, from what you've told me, I didn't expect this to go smoothly. To bad for it. Even if it manages to enter your aegis, it will still be weakened against you.
This is actually surprising. Hum...
Counting on her fingers
So.
Either it has no knowledge of hermetic magic.
Or, it wasted too much time preparing, and will be surprised by your aegis.
Or it was all bluff and no power, as you suspected.
Or... it did the unexpected, but I don't have enough information to make a usefull guess, even uneducated