(Crossing my fingers it’s a plant!!!)

Quillary looks at the others. “So. Friend Spar and Hildigrim go that way (she points left) and that way (right), Jorin of the Bodt and I go this way (straight), and Drusk comes with us, but behind a brace of paces. Yes? Is there ought else we should prepare?” She looks behind her, “It is a good hike yet, perhaps we will have a good idea on the way there. I trust you to act on it, then, because I trust you. Even Friend Spar because she is a friend now.”

Jorin draws his weapons and set its eyes straight ahead.  He nods to Quillary and adds, "We should stay low and quiet as we approach, eyes open and ready." will begin creeping forward as the group moves.

Stealth: 11

The party is able to cross the barren rocky "plain" of the cavern without incident.
(In fact, it seems a little too quiet, but count your blessings.)
It does give the group time to figure out if there is anything that can help your situation.

Your've reached the far wall of the cavern, and see a cave opening. There is the flickering of fire inside, but the entrance curves around, so you can't see more without entering.

The voice in your head says (ominously), "You are in time for the ritual to start. Two more would be useful, and would spare me the effort of finding others. The rest of you can return to the surface with your lives." The mental voice goes quiet, but you hear faint noise inside, like muffled/gagged shouts and pleading.

(This is go / no-go for any preparations.
If there were any long times needed, like Hildigrim using a ritual for Detect Magic, you can say you did it during the approach.
Also last chance for Death Ward or Freedom of Movement from Drusk. Two 4th level slots that can be used.)

Feldspar would like to cast mirror image as soon as Jorin darts into the fray or as soon as she sees a threat. Happy to risk it by casting once we get around the corner no matter what, but if there’s some very non-combat scenario that confronts us she’d hold off. Otherwise she has her blade at the ready and will begin to walk up the wall - how tall is the cave opening?

(Is it off the wall to suggest Freedom of Movement *and* Death Ward on Jorin? That, or Freedom of Movement on Jorin and one other… Quillary or Drusk himself. Thoughts?)

I was going to ask if it took 10 minutes to get there so that I could have cast detect magic, so since you've already said I could, then I did.

If I detect anything I would consider a danger, I'll use message to tell whomever I think should know.

Quote from DirtyDogP >>

If I detect anything I would consider a danger, I'll use message to tell whomever I think should know.

Starting a few feet inside the cave entrance, and extending into the cave as far as you can see, the entire area is covered by an Abjuration spell.

(I think someone asked about some sizes. The entrance is 15’ high and wide. Inside the cave it is 20’ high and wide, but you can’t see past where it curves without actually going around the curve.)

Quillary stops and lets Drusk catch up. “Perhaps now would be a good time to provide Jorin and myself with some protection from being magically impeded. I suspect this creature is adept at magic, and we know it has prisoners somehow restrained.”

(Freedom of Movement for Jorin and Quillary. I shall make a decision since nobody else seems to be. ;)

I'm not entirely clear on freedom of movement...can Jorin no longer be magically restrained or paralyzed, or is it everythign excepting magical retrain/paralyze?

Quote from Guiltysparc >>

I'm not entirely clear on freedom of movement...can Jorin no longer be magically restrained or paralyzed, or is it everythign excepting magical retrain/paralyze?

From the description, spells and magic effects cannot slow down, restrain, or paralyze.

Difficult terrain doesn’t slow down.
Nonmagical grappling (like the banderhobb bite) can be escaped with 5’ of movement.

Oh dang, that sounds awesome! 

Drusk casts Freedom of Movement on Quillary and Jorin.

(If there is the right opportunity for Feldspar to cast Mirror Image, I'll try to remember that.

Hildigrim would have mentioned the abjuration spell he saw inside (post 6156), so you are all free to figure out what you want to do, or if you want to enter anyways.)

OOC: We may need to back up a bit, based on how everyone would react to this:

As soon as Hildi's spell detects the magic, and before anyone can enter the cave (and theoretically before the spells have been cast), the halfling yells, "Stop!" Then, more quietly (but also aloud), "The entire cave ahead of us is bathed in abjuration magic." His voice changes as if he is reciting something memorized, "Magic of this school creates physical or magical barriers, negates magical or physical abilities, harms trespassers, or even banishes the target of the spell to another plane of existence." He finally breaks his stare into the darkness to look at the others. "I know we were planning to cast a few protective spells, but it's possible whatever is ahead may remove the benefits those spells bestow. Before we do that, let's do a few tests with the hope we will uncover what is ahead." Before waiting for a response, he looks around, finds a rock, picks it up, and tosses it into the cave to see if anything happens.

Quillary stops immediately at Hildi’s command. She has learned to trust his knowledge. She watches him toss the rock, following its trajectory with her eyes. 

Nothing happens to the rock.

You continue to hear panicked noises of multiple gagged people, somewhere close ahead (around the bend inside).

Drusk has a 3rd level slot, so he could try Dispel Magic but it might fail. Or someone can look for more clues (one Perception or Arcana check).

Quillary turns to face the cave again. “It is, of course, a trap, but that has never stopped us before. Do what you need, but do it quickly, the souls inside may not have long, I would bring them freedom, or at least peace.” She distractedly puts a hand to the outside of the pocket of her skirtle, as if feeling to reassure herself that something is there.

Feldspar’s eyes dart around the opening, looking for any oddness or clue about what is protecting it.

Perception 20

(I'm going to rule that the FoM spells were cast at the same time as Hildigrim was doing the Detect Magic ritual, shortly before arriving at the cave.
FoM lasts an hour, so we'd want the spells active in case there were any traps or guards near the cave entrance.)

After Hildigrim voiced his concerns about the spell inside the cave, Drusk casts Guidance (rolled a 4 in the Game Log) in preparation for Dispel Magic.
Initially, the cave magic seems like it will resist being dispelled (rolled WIS ability check of 16 in Game Log), but the joy from Lliira's guidance allows Drusk to wipe out the protective magic.

Feldspar is able to see traces of powdered ruby and incense that were on the ground and around the interior of the opening, before they flare up from the Dispel Magic, leaving only dust behind. There were a number of different runes, but one involved repelling Celestials. It would have been unpleasant for Feldspar to enter, but she would have been okay.
(Flavor text: despite the celestial legacy of Aasimar, they are considered humanoid.)
Volo the (spirit) familiar, on the other hand, would have been in trouble flying into the cave.
And who knows what would have happened if Feldspar activated her Celestial Revelation while that spell was active? (While not RAW, I was considering consequences.)

Hildigrim confirms that the adjuration spell that he saw has been dispelled.

Hildigrim reaches up and reactively gives Volo a quick skritch under his chin before following the others further into the cave.

“And now we can go?” Quillary asks, tapping her club to the cat head she wears above her brow. The club glows briefly, like embers, and a fine layer of ash silts off, leaving the club gleaming.

(Shellelagh is cast)

She begins walking toward the entrance, planning to go in.