U2 (a potential cultist) completes his turn without any noticeable effect identified by the party. Within the fog southeast/east of Anearis and Uthal, the unknown (cultists) whisper to each other.

Ura's ears prick and she slowly moves in the direction of the whispers.  (NE, E, NE towards R32).  At all times she would chose to avoid stepping on a tentacled mass.  If at any time she spots a cultist - the man and the woman firing chromatic orbs at herself and the rest of the party - she would attack them in various ways depending on the situation:

- If she spots them from up to 20' away, she will stop moving and throw a dagger, then retreat to be 10 feet south of Uthal, or even further to southwest for the full use of her 30' of movement.  If that brings her into a position near objects where she can BA hide, then she will.  If it keeps her in the open, then she will BA dash for 20' to get to L35 and check on Unknown Individual 3.

Dagger Attack: 8 to hit

Stealth Roll: 12

- If she ends up stepping right next to one due to the darkness, she will stab the cultist with a booming blade rapier, then BA disengage and stop 10' south of Uthal, or even further to the southwest for the full use of her 30' of movement.  If she ends up advancing further and stops next to one, she will not end her turn next to the cultist, either using a BA to disengage and step away as far as possible, or taking an AOO and stepping away far enough to find some cover.

Booming Blade attack: 18 to hit
Damage: 8 piercing + 4 thunder if it moves

- If she spots nothing she will move all the way to T31 under the same conditions as listed above if a cultist is spotted, and should still nothing be visible, then use a BA to dash and circle around the basin and get a lay of the area, using 55' of movement to end up in O35.

... that's a complicated turn.  Here's the Twilight Sanctuary Temp HP: 5

Anearis, still uncertain of the whereabouts of their assailants, decided to stick with his companions. He moves forward trying to avoid the tentacles and the pool he knew was in the middle of the room. (Move to 31N)

As he’s moving, he summons a flickering flame in the middle of his palm, ready to throw it at the first sign of enemy movement.

Ready action: Produce flame (trigger: see an enemy)

(I assume it was my turn, seeing as Austin already did her action)

Ura took only a few steps before being confronted once again by a cultist in the fog. He had been facing Ura's direction, seemingly anticipating the approach, with dagger at the ready. As Ura stepped close (Grid 33P), U2 (Grid 32Q), took a more physical approach and lunged at her with the blade. 

U1: 4

A quick miss, though Ura returned the for with a slash of her booming blade, then leaving the cultist once again in the fog as she disengages.

Austin successfully breaks free from the tentacles with Tide's help, and moves to grid 27L.

From the darkness of the fog, though judging by the sound, very near Anearis and Ura, was the voice of the cultist from earlier. The one who had fled combat earlier. He spoke in a low tone, though both of the elfs were perceptive enough to hear it."He's the one she wants. The rest can perish." 

It was followed by U1 appearing in 31O and muttering an incantation. 

Anearis WIS save: 20

The spell had no effect on Anearis though, and he throws the readied flame at the figure.

Produce flame: 25

If hit: 7 (times 2 for crit)

The flame hits the cowardly cultist and ignites his incredibly flammable robes, as he attempts to retreat back into the darkness.

Uthal swings a massive backhand at the retreating form.

AoO Unarmed Strike: 17 Damage: 4

Uthal will then move forward in the direction that the cultist went. If he finds him he will cast Spiritual Weapon and then Sacred Flame. If he does not he will hold a Sacred Flame in case any cultist enters view.

Spiritual Weapon Attack: 20 Damage: 10

Sacred Flame: Dex Save DC 13 or 8 damage

Moving to 31P, while although having acted to chase U1, it was U2 (Grid 32Q) that Uthal found. The cultist's face bore a look of dread to see the Goliath attack.

17

The spiritual weapon slashed against U2, though he was able to avoid the sacred flame from raining down upon him.

Next to Ura, U3 continued muttering away, concentrating on something unknown to the elf.

With a cultist illuminated by Uthal's twilight sphere, Current squints to make out its position before rushing around, between the tentacles and pool, after Uthal and releasing a long blue tentacle from her hand in the cultist's direction. Tide, having helped Austin get free, now promptly turns invisible before flying over towards Current and flitting around over the genasi's head.

Joining those teaming up on U2, Current moves in to attack. Unfortunately her attempt misses the presumed cultist.

Round 4
Order of Combat:
Cultist? 2 (Grid 32Q)
Ura (Grid 34N)
Austin (Grid 27L)
Anearis (Grid 31N)
Cultist? 1 (unknown grid)
Uthal (Grid 31P)
Cultist? 3 (Grid 34M)
Current (Grid 32O)
Tide (Grid 32O)

"Just hold them off for now. She will devour them, it's only a matter of time." The voice of U1 calls out from the black fog, somewhere on the east side of the room.

U2 took this as reassuring words as he turned towards Uthal and lunged at him with the cultist dagger. 4

A completely unsuccessful strike, which causes U2 to lose the newly acquired confidence and flee east, into the fog.

((AOO allotted to Uthal))

Uthal attempts another backhand swipe with his large gauntlets. 

Attack: 11 Damage: 4

Uthal's swipe finds only air, as U2 flees into the thick, blast cloud.

Keeping away from the tentacle things, Austin starts to open one of the crates to see what is inside.

"Hold them off?  We better put some pressure on them," Ura says as she chases after the cultists, much in the same way she did before, doing much of the same attacking she did before.

If ranged: 
Dagger: 15 to hit
Damage: 6 piercing

If close combat:
Rapier: 9 to hit

Stealth, if possible: 13

Twilight Sanctuary temp HP: 1

As Ura chased the cultists into the fog, she found U1 (Grid 33R), upon reaching 33Q. The abrupt locating of the figure likely caught her off guard, as the quick slash of the rapier failed to land, before Ura disengaged and retreated back behind cover (to grid 34N).

Austin attempted to pry open one of the crates: 19

Within the crate (Grid 27N) Austin finds general 100 feet of hempen rope, a common dagger, parchment, two sets of cultist robes, a cultist dagger, and a golden plated lantern.

Anearis is still unsure of what to do in this blasted darkness. Though he realizes the urgency in Ura’s tone. He summons another flame in his palm. He begins to move deeper into the darkness. At the first sign of enemy contact, he will throw the flame at them.

(Move straight down. Stop at first sight of an enemy or hit a wall or obstacle.)

action: Produce flame. Throw it if sees an enemy

Attack: 19 Damage: 6

Uthal follows the retreating figure into the darkness again. If he finds him he brings his spiritual weapon along and whacks him before burning him with holy fire. 

Spiritual Weapon Attack: 22 Damage: 11

Sacred Flame: 4 DC13 dex

Throwing the flame upon U1, the cultist fell to the ground, severe burns covering his face. With a final breath as he looked up at the elf who killed him, "She is coming, for you." Even through the evident pain on the man's torched face, he held a sinister smile, until he passed.

Moving in the general direction, through the fog, Uthal came to the room's eastern wall would likely be soon, upon reaching 33T. However, going this far, the Goliath failed to locate the cultist (U2) whom fled this general direction.

U3 does nothing different than what he had been doing previously.

Comprehending the words that the cultist is repeating, Current worriedly sends Tide back to check on the last muttering person in the room, who the warlock had just assumed was innocent because they weren't attacking anyone. Meanwhile, she herself stays put exactly where she is and glances around furtively with the tip of a tentacle poking out of the palm of her hand as she waits for something to show itself.

As Tide floats over the fallen pillar, near Ura and U3, she sees for herself, the figure Ura had been spending time with. The robed elf was chained and sat with his back against the stone pillar. He kept muttering something, but the language, or at least the words being said, were not something with which Tide was familiar. 

She was able to pick up a pattern in the speech, that whatever was being said was a long string of syllables  being said over and over again. A repeated phrase or sentences, while the elf sat still, eyes closed as if in deep thought or concentration.