Valar will shake his aid, "Justice will be served, and I will see this darkness is exorcised from the land like a cancer, slicing it away piece by piece." Intimidation 5 

You get the same response from Sanford. Someone will have to try a different approach if you want to interrogate him further.

So what is the plan for the crazed man? If you bind him and take him with you Alsen will volunteer to take care of him, 

Valar looks at Sanford in Disdain. "We need to bring him with us and find someone who can squeeze what information he has in his warped brain."

You secure Sanford and assign Alsen to looking after him.

You awake in the morning and have to make some madness rolls. To be honest, the only people who have to are Amiz and Alsen. Everyone else in the party is either immune to the madness or already crazy: 

Amiz DC 10 WIS Save: 11

Alsen DC 10 WIS Save: 9

Madness Effect roll: 26

You find Alsen in the morning sitting next to Sanford who is laughing. Alsen has his head in his hands and you realize he is weeping while Sanford talks to him. "Your life work is over, your friends have passed on. So should you, give yourself over to the voice in your head priest. It will show you the way, and you will life forever with your friends in Kholias!" While the words are almost gibberish to you, they clearly are affecting Alsen.

Valar will look at Sanford, "Perhaps we need to gag him, and shut him up." 

“I swore no oath, just a promise to do as much good in the world as I can. I wonder if his murder wouldn’t be the right thing. If not maybe just losing a body part. Like I don’t know… a tongue.”

Valar looks at Sanford and does contemplate it. "As I much as I feel he has committed crimes and should pay for those crimes, we should wring as much info out of his rotten head before doing so. Dead men tell no tales, so to say." 

Well I'll let you all decide what to do in terms of interrogation. Alsen will pull himself together after a little while and will still be willing to escort Sanford, but is much more uneasy around the man. 

(I'll give you another day to get info out of Sanford, then I'll move the party on.)

Valar will try a different tactic to get information, persuasion, to see what Sanford can tell them of the threat and the area they are in. Persuasion: 19

And what is it that Valar says to try and persuade Sanford to reveal this information?

Valar will try to persuade Sanford to tell him of Kholias, and the voices he seems to be very familiar with. What is in Kholias now, what is the voice. "Well, you seem to be powerful enough to also face this voice, what is it? Are you allied or friends, or a simple puppet dancing to its strings. I take it you have been to Kholias then, what is it like there that can make you so bold?"

[[I don’t have time to roleplay this out but Thelanis is basically going to be making not really muffled threats about torture and tongue removal in earshot of Sanford.  My intent is to lend assistance to others negotiating with Sanford.  If you need an intimidation roll, here it is: 26.]]

Sanford will fall silent, and then looks up. His eyes are more clear now, no less malicious, but focussed. "What is beheld in Kholias is true chaos, nurtured by Drubax, the Watcher. They guard the entrance to another world. And that gate is growing. It is coming. Intent on devouring this world, and claiming it in the name of chaos." He says this all very matter of fact, as though it was straight forward and normal.

Valar nods in agreement, that once Sanford is speaking like a normal person, and not driven by madness. "A gate you say, like a portal to another dimension, a darker one? This chaos you speak of, does it have a symbol, an eight-pointed star with the arrows pointing outward? What can you tell me of Dubrax, the watcher?" 

Sanford described the Watcher, "It is an alien being, with long fingers and a tentacled face. No imagery, just beautiful images in my mind, of this world consumed. I did find this though." And he pulls out what seems to be a coin, but not from any land you recognize. 

Valar looks at the coin, and to continue with the civil conversation, "Interesting coin, I think I have heard tales of this being and of his kind. They live in a different world than ours, beings of great psychic powers who have flying ships. They sometimes come to our world, to raid and take slaves, thralls I think tales called them"

(Would Valar know of Mind Flayers by name?)

Valar Arcana Check: 18