Might be misses, but in case: 

9 to hit, piercing damage of:

    4

11 to hit, piercing damage including sneak attack of:

9

One of Jairus's crossbow bolts ricochets off the back wall, barely missing Damian.  The other skitters off the floor right next to the rat.

(Kethra, Damian, Tyde, Rubin and Symon are up)

“I feel durn silly shootin at rats, even if they are big ole rats,” Jairus says, as he tries to take aim at the small target. 

Kethra attempts to kick the rat.

"It's not as silly--

Martial Arts: 24 Damage: 7

"--when they're biting you! And you! You better not be another one of those undead!"

Javelin: 16 Damage: 10

(If the kick doesn't kill the rat, she'll throw the javelin at the dead body, not wanting to take any chances with more zombies. Disadvantage because prone dead body: 25)

Quote from LordShadowthorn >>

(Now see, that makes it rather unclear who the vermin is.  The rat?  Or your companions for not moving quickly enough ;)?)

:|

Kethra's might kick snaps the rat's neck with an audible crack, and the last of the beasts falls to the floor.

The passage continues to the north, and there are also three human corpses in this room.

Symon takes a closer look at the bodies, searching for any valuables or other items that might help identify who these people were.  There might be a family in need of closure.

Investigation (if applicable): 23

The corpses have been mostly gnawed down to the bone, but you can tell that it seems the rats weren't the killers—just opportunists.  All three seem to have been killed by a bladed weapon of some sort, probably a dagger.  Each corpse also has this symbol engraved in its skull:

“It don’t mean nothin to me specific like, but we have ran into cult type stuff in some other ruins around here,” Jairus says. “Definitely reminds me of the stuff my ma was into. Pretty sure she was a witch, alright.” 

"Nope," Symon grunts, standing back up. The emblem reminded him of his time with the 'mercenaries' but it's styling was different. "Kind of looks like a tent. Did some deranged outdoorsman do this?"

"Nope, they're cultists! We found a cave where people were raising zombies and dressing them up for fun aaaaand this was one of the symbols that was in that cave."

Drawing her own sword with a silent click, the cloaked girl compares her narrow blade to the blade wound Symon would point out, and her pale eyes open wide.

"Oooh...looks like they're a common enemy of whoever these Delvers are, though," she puts away her sword, then violently stabs her dirty javelin into the wall beside the body's head (to clean it off).

Rubin looks over the symbol. He does not seem too put off by the dead bodies and would take a close look.

(DM, not sure if this is the earth symbol or something else.  If the earth symbol, would it be something Rubin would have been told about from the dwarf cleric's dreams of the earth prophet?) 

(None of you would recognize the symbol.)

Jairus has nothing more to contribute on analysis of the symbols, academic study of the arcane and divine being well outside of his life experiences. He does respond to Kethra’s comment, “We still gotta be real careful like here, just cuz they’re a common enemy don’t make em our friends,” Jairus says, somewhat misquoting a Zhentarim axiom. 

Rubin will shrug and glance to the group.  "Do we continue going north here or do we return to the main tunnel?"

Quote from DragonDenn >>

Rubin will shrug and glance to the group.  "Do we continue going north here or do we return to the main tunnel?"

 "We're here, I say we check this place out thorough, 'fore we go back to the main passage," Jairus suggests.  "I can keep scoutin' for nasty surprises." 

The mysterious smoke starts to swirl around Cat-Davian. Emerging from the plume of geyish black, the druid stands and straightens his cloak. "Well, that was a bit better, but it's still a peculiar feeling changing from one form to another." He wipes rat blood from the sleeve of his armour. "Where to now?" 

Quote from SinarLightwood >>

The mysterious smoke starts to swirl around Cat-Davian. Emerging from the plume of geyish black, the druid stands and straightens his cloak. "Well, that was a bit better, but it's still a peculiar feeling changing from one form to another." He wipes rat blood from the sleeve of his armour. "Where to now?" 

 "Further north here, I'm thinking," Jairus suggests.  "Like I said, we're here already.  We can go check the main path after we clear this hidden-type side passageway." 

He continues leading, looking for traps, ambushes, and secrets, with passive Perception and Investigate 15, likely with Kethra at his side, and possibly more, depending on the width of the passage.

Rubin nods and, gripping his hand crossbow, follows after their scout.

(Apologies for the wait.)

The passage continues north for about 30 feet, then turns to the right (east).  From there, the tunnel opens into a square room. In the center of it, a black rock about a foot across hovers three feet from the floor.

This room is the same size as the last, 30 feet by 30 feet.

Jairus is hesitant to examine the floating rock, assuming it to be clearly magical, and instead searches for traps or other secrets at the perimeter of the room. If the room is otherwise clear, he says, “OK, nothin weird in this room, ‘cept that creepy floatin’ rock. Anyone know what that is?”