"There is an implied 'or else' hanging in the air. Give us Marcus, or else. Don't pretend that there isn't. I get the sense of violence from you, that you know how to handle weapons. And Marcus is obviously adept with combat magics. So, you are some sort of advance team. So, you seem to suggest we are at an impasse, and you offer up the option of us casting spells on you to determine the truth of your words? Tremere lie very well to their patsies. We require more than just a simple spell, and more than a moment of your time."
Tranquillina had been silent up until this point, but she steps forward tentatively and addresses both Jacques and the unknown speaker. "Sodales ... gentlemen ... if it is your primary desire to argue and to tempt hostility, then I shall remain in the background. But if it is genuinely your primary desire to come to common understanding, then I might be able to help." She assumes the least aggressive stance she can possibly put her body into. "More specifically, I know a spell whose effect is exactly that: to help people see both sides of an issue. It would be an act of great trust, I know, to you whom I have just met - er, not even met ... but Jacques - you know and trust me. Will you let me lend my aid in this way?" ((Maybe an Etiquette roll is appropriate here. Com 3 + Etiquette (addressing magi) 3 + stress die 5 = 11.))
Jacques rolls his eyes.
Guernicus lie very well to their patsies. Hope you are ready for that. Lets get on with it.
"My amici and I will retire for a while to allow this one," he points at Jacques, "to cool off a bit." Each of the three touch their belts and disappear. The Jotun does not disappear.
Marcus says from his cell, "Well, that was effective."
Jacques flips Marcus the finger 
What I said was true. They are the blinded man asking what color are their clothes. We all say red and they scoff at us because they are sure they had on yellow. it is an impass until they get off their magic asses and cast some spells to find out the truth. Or get the balls to go out of the Magic realm and see.
"One does not insult the master in his own House. And if they leave the Magic realm, to re-enter the mortal world, they turn to dust, perhaps? Or get hunted down like the dogs that they are claimed to be?"
You mean warden in his prison don't you?
"If that makes you feel better. Sure."
So what's the situation here? Locked in a cage? Guarded by a big giant? ...
Marcus is in his cell. Everyone else is more or less free... But there is a Jotun nearby...
Well then, since nobody listened to what Tranquillina said earlier, she'll see if she can get an idea what's going on. What are the exits from the room? She'll choose one and walk towards it calmly, keeping an eye on the Jotun.
There's one behind the Jotun. And whence the way you came...
Hmm, two exits - one we got there from, a second pretty clearly guarded by the Jotun.
Still, she'll walk to that second one behind him/her. He's at least got to react before she'll stop. She'll keep an eye out for super giant attacks that could hit a huge area, and have her fast-castable Wizard's Leap at the ready - but her Wizard's Sidestep is active and should protect her from one swing at least.
The Jotun speaks and it rumbles throughout the cave, causing the walls to shake, "That path to my home is that way. Proceed at your own risk, you may find making your way back difficult."
Jacques will inspect the cell door that is holding Marcus. Is it a door or just magic bars or a ward?
It's a normal door.
So why don't you come out of the cell Marcus. What is preventing you?
"I play my part. No man can withstand an army on his own. They needed a prisoner, I satisfy the demand for now. When I figured out that they were trying to capture me and not kill me, I became curious as to why. My curiosity is not yet sated. Is yours?"
((What language is the Jotun speaking?))
Tranquillina stops where she is, facing the Jotun respectfully. "Your own home, only? Or the home of you and others of your kind?" She makes a show of peering past the giant down the corridor. "Or, is it the home of those little ones our size who were talking to us just now, and you are simply their guard?"
The Jotun grunts in response to the questions. The Jotun spoke in Latin, and spoke quite well, as a matter of fact.