As you discuss how to proceed, the two men remain deeply unconscious in the nook off the alley. It's a bit cramped here, the uneven cobbles slippery with moisture. A potent vinegar-like smell coming from the dripping vent makes your eyes water. No pedestrians wander by; the scene remains quiet.

Gerrard:

     “I have no special way to charm or convince the Kei look-alike to speak with us, but I will speak to him if you like,” replies Gerrard to Boko, but he adds, looking at Thwack, “But you have had an unusual connection with Kei, Thwack.  Perhaps you should try.”

"Watch our backs," Qivys says as he steps closer to the two captives. He takes out a copper piece, places it on his forehead, and closes his eyes. He takes 2 fingers tocuhes the coin and then points them at fake Kei. He mutters the arcane words and casts Detect Thoughts at 2nd level. Though the spell initially allows him to read surface thoughts, he is looking deeper, hoping to glean anything about this situation and who this person is. 

Qivys probes the unconscious mind of the false Kei. Its brain is alien to Qivys – arcane, artificial, manufactured – and yet quite alive and sentient. It is dreaming – vivid, wild dreams of light and color. This is not Kei's mind. This is not a human's mind.

DC14 WIS Save: 17

This is an evil, selfish, mechanical mind full of plots, paranoia, and visions of grandeur and control. It is working for the wealthy perfumer, Master Loquid, but simultaneously worming its way into the favors of the mysterious Mr. Dory, the enigmatic councillor. Loquid supplies Dory with large quantities of perfume from his shop in the Merchants’ Quarter. Loquid complains about Dory's unpleasant, mildewy odor, but False-Kei has never met him – only doing covert favors for him via his assistants. Loquid has told False-Kei that for inexplicable reasons, Dory floods the inside of his home with water, and keeps stoves burning day and night to maintain the place at a stiflingly hot temperature. False-Kei's mission today, and that of its comrade, Hort, was as bodyguards – to ensure that the delivery of three special new perfumes and a large mysterious box would go smoothly in this dangerous neighborhood.

But the appearance of this new group of interlopers has unnerved False-Kei. It had been trapped for so long in the clutches of the vampiric consorts of Granny Nightshade; when this group appeared and fought one of his captors, False-Kei managed to hijack this new body, as it had done in centuries past, and escape - finding itself in the depths of the ocean, before coming to this city. But after many months, the body's comrades have somehow tracked it here, and that is worrisome.

What Qivys does not detect are any signs of his old friend, Kei.

Qivys breathes deep for a moment then breaks contact. He shakes his head slightly.
"He's gone." he says then tells the others what he has found out. 
"I say we end it's life fer Kei's sake." 

"Who is it? Is it Kei, but taken over by something? Is this related to the vampire? Or our current struggle? What a mess. This whole town. And who is this companion? Are you going to probe him as well, or just end him?" Boko says, gently placing a hand on Qivys' shoulder in an unspoken gesture of support. It's both empathy at the trauma and the loss, but also resolute support for whatever difficult next step the party must do. "We have been running since we got back from scouting the lizardfolk fortress. Unearthing a vampire, trekking into the woods, finding another evil entity, saving children from some unspeakable rite, getting shunted many fathoms deep, surviving unnatural beasts, finding each other on an undead-besieged island, saving survivors from that undead threat, getting back to the mainland 6 months later, ending up here in this mess... is there anyplace in this realm that is tolerable?" She closes her eyes, takes a deep breath, and composes herself. "The only thing to do is the next right thing. If you think this creature needs ending, I support you."

Gerrard:

An unreadable look on his face, Gerrard says, “Thwack has shown us signs of Kei’s…presence…for lack of a better word.  Is it possible that this entity shoved the real Kei out of his body when it took over?  Would Kei’s spirit move to the afterlife or stay nearby, silently observing and occasionally manifesting? If so, and we can banish the spirit inside his body, perhaps the real Kei can return.”

Sighing, he adds, “But that is all conjecture and likely just hopeful foolishness.  Still, if we kill this body, does the possessing entity perish or move along to possess another?”

Thwack 

Amused by Qivys' behaviour, Thwack mimics the gestures of his dwarven friend. He places a coin on his own head and after a few moments shoves two fingers out and touches False-Kei's leg. Nothing happens. "Snarf" he mutters in disappointment. "You does magic's Givers? Me no do..." Before he can finish a giant playing card appears from nowhere. Kei's face on one side and Thwack's on the other. "Yip!" Thwack squeaks in surprise. "Not funny magics Givers. I told you, me no do magics like you or Terry." He sulks as he steps aside and plops down in the filthy alley. "Not funny". The card vanishes.

(Does Qivys tell us about the details of his vision/delve?)

(Yep. "He's gone." he says then tells the others what he has found. )

Quote from Scott_R_Simmons >>

Gerrard:

An unreadable look on his face, Gerrard says, “Thwack has shown us signs of Kei’s…presence…for lack of a better word.  Is it possible that this entity shoved the real Kei out of his body when it took over?  Would Kei’s spirit move to the afterlife or stay nearby, silently observing and occasionally manifesting? If so, and we can banish the spirit inside his body, perhaps the real Kei can return.”

Sighing, he adds, “But that is all conjecture and likely just hopeful foolishness.  Still, if we kill this body, does the possessing entity perish or move along to possess another?”

 "I don't think so lad." Qivys says to Gerrard. "I didn't find anything that was Kei left in there. It's like he's been consumed and replaced. Whatever is in there now is just wearin' a Kei suit."
(Sugar Water!...guess that one)
 "My guess is if'n we kill it, we just release it and it goes after someone else. I say we make contact with our patron an' let them make tha decision. But, we best be quick about it. That other one's just as dangerous so keepin' 'em trussed up and sleepin' is tha best 'cause if'n they wake up we may have ta put an end ta them and not get ta know tha whole story." 

Gerrard:

”Not a bad idea,” says Gerrard, “Maybe we get a cart, cover them up, and make a delivery to the councilor.  We also have the ‘perfumes’ and strange box to deal with these two were supposed to protect, not to mention Mr Dory’s estate that might just have been converted into an Aboleth outpost or nursery.”

"She is going to want two underlings?" Boko says. "She was fairly hands-off last time we saw her. But if you think it best, let us go."

Gerrard:

Shrugging, Gerrard says, “I expect she may be able to learn what they know better than we, but Master Qivys might learn all we need from his reading of thoughts.”

Looking at the other unconscious foe, Gerrard asks, “What about this Hort fellow—are you willing to risk reading his thoughts, Master Qivys?”

"I think tha nature of the two would get her attention." Qivys says. "They are agents of an opposin' house an' are a threat to tha folks here."
Qivys pauses.
"I could be wrong." he says with a shrug. 

"I'm kind of hesitant ta read his mind." he replies to Gerrard. "But I can try if'n ya believe it will help. Just give tha word." 

Gerrard:

"Maybe just surface thoughts.  If the Aboleth is in his thoughts deeply enough to evoke magic through him, it might be dangerous to go deeper," suggests Gerrard.

Qivys nods and steps to the other man.
He takes the copper coin, touches it to his forehead hen points it at the unconscious man, and reaches out to the other man's mind.
(assuming it hasn't been 1 minute. If so, Qivys will cast the spell again if needed.)

Thwack 

While he waits for the tall ones to conduct their brain scanning, Thwack watches the alley for any curious citizens. "Me watch out so you can magics Givers. I no let anyone stick face in our jobs" he says, a satisfied grin replacing his sulking pout.

Perception 20

Thwack keeps lookout. He spots a middle-aged couple walking through your alley, but if they notice anything in your nook, they seem to pay no mind. They look like a couple of locals. The pair continues walking casually down the alley and finally rounds the corner.

Qivys probes Hort's unconscious mind next. Qivys finds him to be – as far as he can tell – fully human. He dreams of fishing.