"He is hearing you, and will answer," He replies, then looking around the room at the artifacts on the walls, "I just need to find that tiara."

He then walks around the bar to the south wall and starts looking, "Could you help? It's a small silver tiara with turquoise gems in the crown." 

Carlin obliges, helping him look around.

Investigation: 16

You find on the walls a plaque below a red rod with each end resembling carved red dragons, which says, "Blast Scepter: Taken from Halaster Blackcloak in the Mad Wizard's Lair by Jasper Copperkettel."

There's another nearby plaque with a petrified human skull, reading, "Nester's Cranium: Former former apprentice of Halaster Blackcloak, petrified by Lia Liadon in Dweomercore."

Another such plaque below a manta-ray shaped cloak says, "Cloak of the Manta Ray: Owned by Henenu Bakafre."

Another says has a shiny shield as reflective as a mirror, saying: "Mithral Shield: Used to deflect Xanathar's Eye Rays in the Raid of Xanathar's Base by Alberich Trollbleeder."

You don't come across the tiara, Carlin. 

(Also, just a note, nothing above is a typo. Everything written on the plaques are written as above.)

"Huh... well it's not over here," Carlin says, looking over all the artifacts. "Any luck?"

Erdan mumbles, "Stuffed space hamster, invisible dagger, tarrasque blood, nothing over here, anyone see it?"

Fen is sure he remembers seeing a tiara and scans the room [unmodified d20 roll:11  if I can use Perception it is +5 so 19,  if  Investigation it is +1 so 15]

(It's investigation)

Fen finds a doublesided blue-steel javelin with lighting shaped points, with a plaque that reads, "Javelin of Lightning: Used by Henenu Bakafre."

You also find a pair of owl shaped goggles that has a plaque below it that says, "Goggles of the Night: Crafted by Alberich Trollbleeder."

There's also a spellbook in a glass container stuck to a wall with a plaque that says, "Mad Mage's Spellbook: Containing every spell in existence."

You don't find the tiara. 

Fen says [whilst continuing to search - let me know if I should roll investigation again] "I've always meant to ask you about how you came across these wondrous items. Can you yell me the story of the Javelin of Lightning and Henenu Bakafre while we look for the tiara?"

Erdan continues mumbling while he's looking, distracted, and it takes him a minute to register that you were talking to him, "Oh, sorry yes. Henenu was the leader of our party. He's a paladin of Torm, he's the one that built that huge stronghold in the middle of Waterdeep in between sea ward and north ward. You must've seen it."

[DM question, has Fen seen the stronghold? If so, he says he has. If not he just continues trying to get more information about the Javelin and Henenu Bakafre while searching for the tiara]: "So how did Henenu come across this Javelin? What does it do?"

(All of you would've seen the stronghold. It's a huge stone fortress with statues of paladins and Torm, with banners of the Lord's Alliance, and is the second largest building in Waterdeep.)

Erdan thinks for awhile, then replying, "We were in Undermountain, had just killed some creature, I'm not sure what, but we took it from their treasure hoard. It can be used as a magical javelin, and they can transform into lightning periodically."

Rinzak's eyes grew wide at the display, muttering under his breath in his own language for a moment before clearing his throat. With a soft wave of his hand and a muttered phrase an invisible hand of magic appears which he uses to sift through the items and otherwise aid his search as he asks "Might the good Lif be able to answer if that was a display of Dunamancy or comparatively mundane levitation?" A bit of a boorish tone to the latter as though if that is accurate he would be bored with the answer. He simply listens in on the conversation about this Javelin as modified martial weapons were of little interest to him.

Investigation Roll: 12

"It has to be around here somewhere," Carlin murmers, "Someone didn't take it did they?"

Quote from BaconExpert982 >>

"It has to be around here somewhere," Carlin murmers, "Someone didn't take it did they?"

 "I'd know if someone took anything," He says, "They'd die, and I'd be alerted."

"That's... rather violent," Carlin says, looking around, "but I suppose understandable. Could you not get in trouble for that, out of curiosity."

Fen asks "Does your poltergeist friend act as a security system then? I always wondered why none of the shadier looking long term patrons ever tried to do a 'grab and run'."

[Even though Fen is a 'charisma-talky' type rogue rather than 'pickpocket, rob house' type rogue, even he was tempted by these powerful artifacts.]

Quote from BaconExpert982 >>

"That's... rather violent," Carlin says, looking around, "but I suppose understandable. Could you not get in trouble for that, out of curiosity."

 "Anyone who would take an item from these walls knows that it's thievery," Erdan says, "Also, even if we didn't ward the items, they probably would kill themselves and many others with them. It's for everyone's safety. We don't have to worry about the legality of it. You've heard of Durnan, right? The deceased owner of the now destroyed Yawing Portal?"

Quote from Zegethys >>

Rinzak's eyes grew wide at the display, muttering under his breath in his own language for a moment before clearing his throat. With a soft wave of his hand and a muttered phrase an invisible hand of magic appears which he uses to sift through the items and otherwise aid his search as he asks "Might the good Lif be able to answer if that was a display of Dunamancy or comparatively mundane levitation?" A bit of a boorish tone to the latter as though if that is accurate he would be bored with the answer. He simply listens in on the conversation about this Javelin as modified martial weapons were of little interest to him.

Investigation Roll: 6

 You search the walls, finding the following items:

The first item is a jar, filled with a black liquid, almost like a shadowy fluid. The fluid seemingly tries to escape from the jar, moving around, semi-sentiently, with a plaque that says, "Shade-fluid: Harvested by Alberich Trollbleeder."

The second item is a large dodecahedron made of gears with runic symbols on each side, hidden inside a glass container with a plaque that says, "Dodecahedron of Power: Do Not Roll"

The third item is a boomerang engraved with marks of wind, that reads, "Boomerang of Returning: Crafted by Alberich Trollbleeder"

The fourth item is a pair of golden-glassed goggles, that says, "Ordinary Goggles: Found in Undermountain"

(You don't find the tiara)

Erdan replies, "Oh, poltergeists are just telekinetic. "

Quote from MaxandDad >>

Fen asks "Does your poltergeist friend act as a security system then? I always wondered why none of the shadier looking long term patrons ever tried to do a 'grab and run'."

[Even though Fen is a 'charisma-talky' type rogue rather than 'pickpocket, rob house' type rogue, even he was tempted by these powerful artifacts.]

 Erdan replies, smiling slightly, "I'll explain the system to you, as you're clearly newer to the tavern, and don't know as much. As you would know if you talked with an experienced patron, every now and then some petty thief will come in the tavern attempting to make away with one of these items. When they touch the item, intending to steal it, their heart stops, and they instantly die while screaming. Their eyes turn black, leak dark liquid, and they are dead within seconds. If someone is just curious when they touch the items, they receive a shock and telepathic warning. Some people bet on how long they can hold a finger or hand against one of the items. Some of them find it quite amusing. Unfortunately, we occasionally have a waitress that brushes up against one while holding food or drinks, and accidentally drops them, but the patrons find this humorous."  

"... huh..." Carlin says, not sure of the ethical nature of the security system but goes back to looking, "do you remember what plaque it was on?"