Pin it to the table, yes. Spread like for a crucifixion. It doesn't matter if he pulls free. You just need to be ready to catch him.

“Ah.” She does as directed, making use of the dagger. “That makes sense I guess?” She presses her sword fully half of its length into the table because it would be REALLY inconvenient if he could make use of it in any way. “This is a lot more fun than being the one affixed to the table,” she says to no one in particular. 

Understandable. Tell him we'd like to hear about his faith. He should explain himself. Who is his god? What do they desire?

“My god is the Doom of Agraphael,” the priest’s back arches in religious fervor. His hands tear where they pull against the blades transfixing him to the table. “The breaker of towers! The lord of the deeps! That which comes from the seas, that which brings the pounding surf. The god of madness and the god of drowning.” He speaks names then, but names which it is impossible to understand or remember or even to write. Names which have no related sounds any human mouth is capable of forming. 

The girl abruptly recalls a story told to children in Ardholm:

Recall the Doom of Agraphael, which came upon them in the Summer of the Long Grass, year three hundred ninety first of the twelfth age. Recall their high walls and their shining towers. Recall their proud castle on the shores of the Narrow Sea. 

Recall their golden fields of grain and their verdant hills and their cheery farmers; recall their strong keeps and their sprawling colleges and their proud warriors and learned arcanists. Recall the great works of Agraphael and recall when they were cast into the sea. 

Recall the welling tides and the pounding surf and recall the Doom of Agraphael. 

Recall when men went mad and offered up their sons to the Lord of the Deeps. Recall when their soldiers threw down their arms and danced naked in the streets. Recall when their priests profaned their alters and beggars ate their kings and Doom came to Agraphael. 

Recall when fruit rotted on the branch and fields wilted unplowed and the sea came to Agraphael. When ships were snatched from their harbors and dashed across the peaks of the tallest mountains. When waves threw down the highest walls and the proudest castles and Doom came upon Agraphael. 

Recall when the seas retreated to their shores and the Lord of the Deeps returned to its ocean bed and slumber came upon the Doom of Agraphael. Recall how once-green hills had become dunes of sand and fields of grain had become bowls of dust and cities had become tombs. 

When your child asks, “why fear the sea?” look upon them and say, “Recall the Doom of Agraphael.” 

The girl is now very extremely alarmed. 

Hah! Do not lose your nerve merely because a foe is strong! You are weak, girl! Even with my stolen might carved into your bones! Rejoice in it! This one serves the deep, so we shall offer him its blessing. Fetch water from the basin.

The girl fetches water from the basin, silently, but her thin hands tremble. Chestnuts… Do what the voice asks. Do it right, and… chestnuts. And these people- these cultists- need to die anyway, no matter what they worship or else sister will be so disappointed…

Tilt his head back, and his chin up. Hold his head still, pour water onto his face. Into his nose.

He sputters and thrashes as the girl does as directed. Her trembling hands slosh as much water on the floor as in his mouth, but it is a big basin. 

He is welcome to thrash, and she is welcome to spill the water. After a little while, the voice will direct her to break some bones in his foot, before returning to waterboarding. Then break another rib.

She does as she’s told, because there are chestnuts in her future! 

In between the buckets of water, the man gasps and splutters out profane prayers. 

After a while, the voice starts encouraging some personal volition. Would he rather some more water, or a punch to the gut? Can he demonstrate a sermon? It will hurt less if he follows along.

It takes a very long time, but eventually the man does. Somewhat. He will happily begin a sermon- crazed ramblings about how drowning is the most merciful of deaths, about how insanity is freeing, about how the grain has no right to fight the scythe. 

He overwhelmingly prefers blunt force trauma to more water. 

The voice hasn’t insulted her in a while and this is good! She’s trying her best. 

She is also happy to explain exactly how not-freeing insanity is. 

The voice is happy to permit the two to chatter about the relative merits of insanity. Eventually, it will begin offering the choice. "Renounce your faith and you can have another broken rib instead of another minute of drowning." If the cultist rejects the offer, it shall improve. This produces a virtuous incentive gradient where the man is encouraged to accept more pain.

It takes a long time. A very long time, and many basins of water. 

“For a worshipper of a drowning god,” the girl speculates, “it seems a little heretical to want not to drown?” She enthusiastically pours another bucket of water on his face. “But then again, I’m a Royalist, not an Ardist. Religion isn’t really my strong suit. Stabbing is. And pouring water, apparently.”

Eventually, between bouts of coughing and gasping, the priest renounces his faith. 

"Good, good. You've done well."

A cult leader will have a healing potion around somewhere. There is mortar missing from a stone next to his bed. Move the stone.

Good? Good! She did good! The girl dances over to the stone, moves the heavy lump with a twitch of superhuman muscles, and finds a tiny stash of potions in the damp alcove beneath. A broad squarish bottle of something translucent and ochre. A tiny diamond-shaped bottle of something opaque and quicksilver-golden. A handful of rounded teardrop vials of something iridescently green. The crimson wax sealing the corks is stamped with the crest of the trading house O’niel. 

The voice didn't mean her, but neither is it paying enough attention to correct the misapprehension.

You don't have a scroll for this one, but it is simple, your body is strong enough for it. Repeat my words phonetically and exactly.

The spell is twelve syllables, a simple piece of magic detection.

She does the magic- almost botches a syllable because… well… chestnuts! But the spell takes, and meaning twists into their shared mind. 

In order: Owl’s Wisdom, Fox’s Cunning, and Lesser Heal. 

Remove the blades and feed him a healing potion. We need him more presentable to meet the flock. Take the other potions with you. Ask him if they had any plans for this evening.