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.

She does as directed, and the priest’s wounds flow scarlessly closed. 

There is a celebration of the tides tonight, in which the majority of the flock will be in attendance. Those whose duties as city watch wouldn’t make their absence notable. 

They also intend to sacrifice a slave via drowning. The priest speaks about this at length and with great anticipation.  

"Oh, how wonderful! A sacrifice! Who is the slave, someone worthy?"

Just some half-elvish healer without any meaningful power. Her mother was supposedly taken from Dath Lomin itself, and her father was a sailor aboard the Shell Islander slaver’s galley that captured the mother. This is why the daughter was selected for sacrifice: an eternal life sacrificed is a greater gift than a mortal one, and someone conceived aboard a ship is a fitting sacrifice to the lord of the deeps. 

"Oh my! What an amateur mistake! Perhaps I could have expected no better of one who would renounce his god over a little pain. No, the worthiest sacrifices are obviously those that have the most faith. Now who in your little congregation has the most faith, do you think? No, don't look so concerned. It couldn't be you. You renounced your god, you are nothing to it now."

“…” the priest says. He rubs at his now-healed wounds. “That would be the Speaker for the Sacrament of Drowning…. Err… he gives the lesson while I…” he glances at the basin. 

"Hm. I'm not sure I trust your assessment of his character. I would have figured you were worthy, after all. Who's to say he'll do any better. We should check. Take us to him."

“He is in the storage room with the slave… ought I to call him, or… I’ll take you to him I suppose.” 

The storage room is larger than the priest’s quarters, but not by much. Mouldering crates lie all about, as well as a not-quite-large-enough rust-reddened cage. A bound, gagged, and blindfolded half-elven girl trembles within. A large man in the same profaned ocher robes sits on a crate nearby, scarred hands whittling away, a small mountain of wood shavings about his feet. 

"He has potential, but he'll need to be tested. Explain the issue to him."

The priest explains with that deep compelling orrator’s voice- about how the Doom requires a worthier sacrifice than a slave, about the speaker’s peerless dedication. 

The speaker stands proudly. “I would be honored to serve,” he bows his head.