...And it is Kei's psychic strike that does it in. Kei finds its alien mind somewhat tough to penetrate, but rather soft once he does. 

The creature is dead. Combat is paused. One calm, mesmerized manticore remains.

Everyone may act.

Gerrard:

Looking at the manticore and considering, Gerrard grabs the rope he was planning to use to arrest the winch mechanism and uses it instead to tie up the manticore.  Given the nasty tail spikes, he uses the iron rod to pin the tail to the ground so it hopefully won’t be able to attack that way.

Sleight of Hand to tie up the foe:  8

(Odd, my post from the previous round didn't seem to stay up, I'd just cast aura of vitality and wanted to heal Gerrard: 10)

If you'll allow that to still have happened, she'll heal again: 8

And ready a frostbite for anything hostile: 10 cold on failed CON17 save

Kei 

When the red frogman collapses, Kei walks casually towards the drooling manticore just in time to see Gerrard attempting to tie its limbs. He offers help with the ropes. Spying the rod he remarks to himself "So that's what that is" then to Gerrard and Boko, "What now? I don't think that thing will be open to chit chat" he nods towards the incapacitated monster. While waiting for a response he heads to each corpse and checks for anything of interest.

Gerrard:

”Thanks,” says Gerrard as Kei helps with the ropes, “I’d prefer not to kill it unless we have to, but unless we can nail it into one of these crates we may have no choice.”

Advantage roll on Sleight of Hand:  20

Quote from rkmobius >>

(Odd, my post from the previous round didn't seem to stay up, I'd just cast aura of vitality and wanted to heal Gerrard: 9)

If you'll allow that to still have happened, she'll heal again: 8

And ready a frostbite for anything hostile: 15 cold on failed CON17 save

 (Gerrard is only down about 5 hp, as he was able to parry most of the damage in melee and the ranger attacks missed, so you may want to do a lesser healing spell or hold off).

As the hypnotic spell ends, the manticore shrieks and squirms against Kei's and Gerrard's restraints. Boko prepares to freeze it if tries anything offensive. DC16 Acrobatics check: 5 

But it is firmly held. It roars with anger. "Trespassers!" booms its eerily humanoid face. "Thieves! Attackers!" 

Gerrard:

In an oddly controlled tone, Gerrard intones, “You are defeated and your behavior now determines if you will also be deceased.  Choose your next words wisely,” as he holds his burning dagger and glowing rapier at the ready.

Intimidation:  24

The manticore glowers at Gerrard. Contesting DC13 charisma check: 1

The creature grumbles and goes quiet.

Gerrard:

”That’s better.  We are here to speak to your master—no, not Mister Dory—your true master.  Tell us what you know of the operation here and give us directions to your superior,” says Gerrard calmly.

(Thanks, I thought you'd been hit a lot more! Switching to healing word for 7hp on Gerrard.)

"That was well done," she says to Gerrard. "Welcome back," she says to Kei.

How easily could Boko get up to the second floor? There's the big open thing the manticores jumped through and the frogman fell through, and no obvious stairs?

Can she go over to the frog body and search it?

Kei 

Reinforcing Gerrard's statement, Kei offers his own observation. "As you've seen, your kind is no threat to us whatsoever. It would serve you well to heed my friends words and answer truthfully." He uses Prestidigitation to enhance his words with plumes of illusionary smoke flit about his head and shoulders as though his temper is burning the air around him (similar to fiend may have smoke rising from their skin).

(Kei: Make your own Intimidation check!)

Boko looks up. The large square hole above marks a second floor about 20 feet above where you are now. But there are also two iron spiral staircases that rise from the northeast and southwest corners. The red frog thing carries nothing at all. Its massive hooked claws leak foamy black liquid.

"You are trespassers..." growls the tied-up manticore. "We are guards. Mr. Dory is our boss. No others. Not Chumwell. Not scum. Dory."

Kei 

Intimidation 24

Gerrard insight on the reply:  12

Boko offers to go up either staircase to take a look…

The manticore's gaze alternates between Gerrard and Kei anxiously. Gerrard doesn't sense it is lying – just angry, fearful, nervous, and a bit righteous. 

Boko eyes the two identical spiral staircases in two opposite corners. 

Gerrard:

Nodding at Boko to go ahead and explore if she would like, Gerrard says to their captive, “I suppose it does make sense that they would keep you in the dark about their true purpose here and the nature of the aberration actually in control.  After all, a job offer to ‘come guard the warehouse where the deep sea Aboleth corrupts the city leadership into poisoning their home and sends aquatic minions to murder the citizens’ doesn’t sound as appealing as ‘come work for the councilman’.”

Continuing, he says, “Lantern murders and Harbor ‘ghosts’ are no coincidence, and neither are waters slowly growing more and more foul—we will save this city from this threat if we can, but I believe you are an unwitting dupe, not a co-conspirator.  If any of this rings true to you given what you have seen here, I ask your help in destroying the Aboleth and restoring the council members to their right minds.”

Persuasion:  23