The monster screams out in pain at the hit. It's not dead yet, though. Kessintra's turn.

Kessintra slips into the room and up to the bugbear, switching to her shortsword and newly acquired scimitar.

Action: shortsword to hit 19, damage 7 + 8 sneak attack (since Zan is also within 5 feet)

Bonus action: scimitar to hit 8

That shortsword dealt the hit that broke him. While not dead, it is on the ground, its life flashing before its eyes. It calls out to you in a deep growling voice, speaking broken common.

"Wait! Spare, please! Bargain!"

Kessintra stops just short of finishing it off, staring coldly.

"You control the owlbear. How?" She demands, blade hovering at his throat.

Garrick aims his crossbow at the downed warrior. Speak your peace. What you say will determine whether you live or die. The atrocities you’ve committed must be accounted for and repaid.

The terrified monster addresses Kessintra first. 

"Me send traitor. Traitor eaten. Beast fed."

He then turns to Garrick.

"No 'atrocity'..... Me just survive."

Who are the traitors?

"Simple enough then. Let's toss him to the creature." Kessintra states with a shrug, looking to the others.

He quickly responds to Garrick. 

"Other goblin. Try take throne. Fail."

It takes him a while to process Kessintra's suggestion, but when he does he immediately protests.

"No! Anything! Serve? Me serve!"

This "man" is not necessarily evil, Garrick says while looking at Kessintra. Don't judge him the same as the goblins. We know they have done wrong, but what do you truly know of him? To the Bugbear, Stand and tell me your name. What have you been doing here?

"It has only tasted goblin flesh, then? Perhaps the beast can help us with the lower levels." Kessintra looks encouraged, ignoring the bugbear's pleas completely, but allowing him to get up since Garrick seems set on it. When the prisoner inevitably does something stupid, she'll be there to strike him down.

"Well..."

Amelia places her hand on her sword, her eyes narrowing.

"... Besides how to tame the owlbear, I also want to know about the deity you and your people worship. Answer our questions honestly and We might free you. "

Amelia’s eyes glow with a divine light, attuned to detect the hint of deception.

Insight: 18
Guidance: 4

Ah Kessintra brings up a good point, we also need more information on this building. How many goblins are here and are there floors below this one?

Zan stands over the creature, what of the alter? What kind of ceremony was taking place?

His eyes dart all around you. He seems overwhelmed, but replies anyway. He doesn't stand.

"Me King Grol. Me lead goblins. We find castle. This only floor. We pray. To Maglubiyet. Lhupo do pray. Him and two other pray every day."

He's being sincere. He wouldn't lie with his life in your hands.

"A castle with no secret levels...?" Kessintra can't hide her disappointment at the news, sighing as she turns her attention to searching the room.

Perception 21

Whispering to the others, If he is truly a king, having him owe us a life-debt could be beneficial. I say let's try to get as much information and loot from him as possible, then let him go -- but we need complete agreement on whatever we decide. We also need to resolve the issue with the owlbear.

"I do not understand killing the goblins but sparing the one who commanded them. Still, I would let the owlbear live...Let him take it with him, so it can continue being fed as it has become accustomed to."

To Kess, I think the answer to this next question will determine what we do for good.
To Grol, If we release you, what will you give us in return and what do you plan to do afterwards?

Insight: 19

"I....."

He seems to think for a moment, unsure of what he would give you all. 

"I give chest! In beast's room. Scrolls and gold and bottle. Then I run."