You don't detect anything with divine sense, and despite Mal'thrae doing the running man up the hallway, you are able to get through with no issues.

You climb some staird, and threadbare curtains hang on the east wall of a long hall, in the middle of which a muscular half-orc in dingy robes stands with his foot on the chest of a male human with wavy red-blond hair. Fire burns around the orc’s clenched fist, and his victim cries and squirms helplessly beneath him.

Seated on a raised platform to the south is a nightmarish figure wearing black robes. It has large white eyes and rubbery purple skin, with four tentacles encircling its inhuman mouth. It cradles and gently caresses what looks like a disembodied brain with feet.

Rayner: "By Torm's name , what is that tentacle creature!? We need to help Master Floon, he's in danger!"

"Oh, so that's who you've been busy with," Melody says, storming into the room. "Hi there Grum'shar, miss me?"

Mal'thrae draws his bow. "The duegar took six seconds. The human took one. The goblin never even woke up before he died. How long do you think it'll take for you?" he calls to the half-orc.

Auric:

Auric charges in, ready to knock that laughing half-orc off the helpless man matching Floon's description, saying, "We are here to rescue you, Floon!"  As for tentacle face and the brain, he'll deal with that when he must.

At the intrusion, the tentacled creature rises, sets the brain-thing down, and starts moving off to a side hallway. Grum'shar jerks up and snarls. You'll find me a much tougher challenge...there's a reason I'm the boss.

Roll initiative!

"The people you hired suck, your lair doesn't have traps, there's an ooze in the closet that you haven't dealt with, your armory is a mess, and you have symbols that paint the sewers all the way here. You're a terrible boss, Grum'shar. Get your life together."

Mal'thrae initiative: 15

Initiative: 21

Rayner: " Time for you to retire and leave this life of a thug wannabe. Please release master Floon or suffer the consequences of your actions, tooth-face!"

Auric:

Initiative:  14

Initiative: 18

Valen initiative: 7

Urukar Initiative: 8

Grum'shar: 12 brain thing: 4

Rayner, Melody, Mal'thrae, Auric

Auric:

Charging over to the manic half-orc, Auric swings his battleaxe at the creature, trying to sweep him off the injured Floon's body and deliver a telling blow at the same time!

Battleaxe:  Attack: 7 Damage: 8

Rayner runs to Grum'shar and tries to tackle him.

Shove(Prone): Skill (Athletics) : 10

If Grumshar is knocked prone by Rayner, Mal'thrae will move next to him and stab with his rapier.

Attack: 19 Damage: 8

If Grumshar is not knocked prone, he'll shoot at him instead.

Attack: 12 Damage: 10

Grum'shar athletics: 8

Grum'shar's flames around his hand die as he dodges Auric's swing, but he's too distracted to see Rayner's shove and he goes sprawling. Mal'thrae takes advantage and stabs him in the stomach, severely wounding him.

Casting Vicious Mockery: Wis Save 15 or takes 4 psychic damage and has disadvantage on next attack roll.

Melody laughs at him and calls out, "You are the feces that's made when shame eats stupidity! You should have just let me leave dumbass!"

Grum'shar wis save: 4

Grum'shar's eyes widen as the words fill his mind and the enchantment takes hold. They glaze over, and he goes limp, blood now pouring out of his ears as well.

Urukar, then Valen.