They made relatively good time for a short while, until Clavius began to slow them down. The thief could barely walk, and he was holding his stomach.

Clavius: Urgh...
Bosco: What's wrong?
Clavius: Don't know... (he doubles over) Pain...hurts...argh!
Mongo: (grabs the man's arm and gets under it, supporting him) I've got you...easy.
Ged: Quickly, lay him down.
Mongo: (does so, with the help of Gorin)
Clavius: Ungh... (he begins shivering)
Arnold: Whad's wrong with him? It's nod even cold in here.
Peldor: Get him some water!
Clavius: (begins frothing at the mouth) Urrrrrrghk!
Otto: Looks like poison, if you ask me.
Belphanior: (frowns) Maybe he got exposed to venom at some point.
Tanya: (shaking her head) I don't think so.
Clavius: (suddenly begins convulsing wildly)
Ged: (casting a spell) I'll try to neutralize poison!
Tanya: But-
Clavius: (arches his back, then slams back against the floor, hard)
Belphanior: Hold him down, before he hurts himself!

Arnold, Mongo, Gorin, and Belphanior held the man down now, but they couldn't have anticipated what happened next.

Clavius: (arches his back again)
Belphanior: Whoa!

A dark stain was spreading across the front of Clavius' tunic, and his struggles suddenly doubled in strength.

Clavius: AAARGH! (he bucks, fighting with all his strength) AAAAAARGH!
Belphanior: Damn, he's strong!

The man's chest, just below his ribcage, exploded, spraying Belphanior and several others with blood. A small, fanged head now protruded from Clavius' stomach, blood and guts dripping from its slick form.

thing: Screeeee!
Tanya: (gags)
Lyra: My...gods...
Otto: What in the hell...?

The monster, whatever it was, didn't offer any answer. Rather, it emerged fully from the corpse of Clavius, a single powerful leap pushing it out and past the shocked adventurers.

thing: (slithering away with great speed thanks to a long tail that just became visible after full emergence from Clavius' stomach) Screeeeee! (it vanishes into the darkness)
Ged: B- Boccob!
Otto: Don't just stand there - get the thing! (he hastily works his crossbow)
Bosco: Uh... (he looks at Otto, then at Clavius' bloodstained body, then back to Otto, who is aiming into the darkness)
Otto: (lets his bolt fly) Damn! Missed!

Only a faint cry echoed through the vast tunnel, reminding them that the thing had made good its escape.

Alindyar: Perhaps I should fly after it...
Otto: Forget it. There're too many nooks and crannies here - it could hide anywhere, and you'd never see it.
Ged: (to Belphanior) Perhaps your sword-
Belphanior: (shaking his head) Whatever that thing was, it had no soul. Blackrazor never knew it was there in the first place.
Tanya: (still choking) Poor Clavius...
Songa: (tightens her grip on her spear) This bodes ill.

They didn't want to leave Clavius' corpse out in the open to rot, so they put it into a thick sack and moved it to the side of the tunnel. There was an awful lot of blood, and the horror of what had happened - right before their eyes - still lingered in their minds.
After the gory task was completed, they had to decide what to do next.

Ged: Okay, we need to figure out what we're dealing with here, and quickly.
Belphanior: Well, obviously that...thing got into Clavius' body somehow. Maybe that's what happened to Renfield.
Peldor: But we don't know that. The other four were killed by something else...
Otto: Given what Clavius told us, it sounds like he met the same fate as the ogre mage his group found.
Songa: Which means there are two of those small monsters running around.
Peldor: As well as something bigger.
Alindyar: (shaking his head) Something is not right here.
Tanya: No shit. (to Lyra) Why don't we just teleport out of here, get some reinforcements, and come back.
Lyra: (nodding) I wouldn't mind.
Belphanior: Oh, come on! We've come up against stranger - and more dangerous - places and monsters than these. We never gave up before and we won't now!
Ged: Much as I hate to agree with you, you're right. We've got no reason to leave yet. We need to find out what happened to the other party, and we need to find the artifact we were sent here to retrieve.
Otto: (frowns to himself)
Peldor: (to Tanya, quietly) This is the last time we do something like this. Things are already out of hand.
Tanya: (nods, then draws her sword, checking its edge)
Rillen: (strings his bow, determined to be ready for whatever might attack them next)

They moved on, torches and lanterns and other light sources shining brightly. The light made them feel better, though it surely also made them visible from far down the tunnel. Still, they preferred it this way, for nothing would creep up on them under cover of darkness.
The trail of blood and slime from the thing that had hatched from Clavius' belly didn't go far, and they had no way of knowing exactly where the monster had gone. However, it wasn't long before they came upon a small shaft in the floor. Barely four feet wide, its edges were rounded, smooth. The blue mist that sheathed the lower parts of the tunnel's floor was here, too; in fact, it prevented a clear view down the shaft.

Bosco: I wonder if this is what Clavius was talking about.
Songa: I don't know, but you may be the only one who can fit in the thing.
Bosco: (eyeing the vertical shaft) Hmm. (he thinks about treasure and weighs that possibility against the risks) Okay, I'm going down. (he makes ready to descend)
Peldor: Wait!
Bosco: Huh?
Peldor: Tie a rope to him.
Ged: Why?
Peldor: Just in case. We'll tug three times, at brief intervals. If all is well, tug back three times, and we'll know. If we don't get three tugs back, we'll know to pull you back up.
Bosco: Oh. Hey, that's a good idea.
Belphanior: Here's a better one: I'll follow him down. If he gets himself into trouble, I'll blast the shit out of whatever's down there.
Bosco: (nods) I like that idea too.
Otto: Well, do both, then.

Shortly, Bosco entered the shaft, and Belphanior tied a second rope to himself before following the halfling down.

Otto: You sure about this?
Belphanior: No sweat.

With that, the elf descended after Bosco, quickly vanishing into the darkness of the shaft.