As her confusion lifts, Chikra goes into a rage and dives at the Sidereon with her longsword. Attack: 15 Damage: 10.

Krusk is going to thrust his Pike +1 into the Sidereon.

To hit: 8

Quote from StevenDeeds >>

Vor, give me a dexterity saving throw to see if you can get it from Lia while she is confused.  DC 12.

Feeling especially threatened by Vor and Lia. the Sidereon casts eldritch blast creating two bolts of energy at the pair.  The confusion lifts, and everyone can take actions in the room.

at Vor - Attack: 15 Damage: 7

at Lia - Attack: 11 Damage: 7

 Lia did not have the key.  She let the one who cast the ritual have the right to take it. She never touched the key.

Hallanann will place the key in the keyhole and turn it.

Inserting the key and turning it requires using an action to attempt a DC 15 Dexterity (Sleight of Hand) check.

Hallanann 8 vs DC 15

The sidereon vibrates and shakes as it spins and whirs.  Light comes and goes in the room as the sidereon warps energy in and out of the planes.  With everything going on, Hallanann isn't able to get the key into the hole.

The blows delivered by Chikra and Krusk seem to glance off the machine with no effect.

The sidereon casts eldritch blast Hallanann and Krusk

at Hallanann - Attack: 9 Damage: 3

at Krusk- Attack: 16 Damage: 4

As soon as Hallanann is able, he is going to make another attempt.

Sleight of Hand: 17

Hallanann slides the key into the slot and turns it.  The sidereon bellows and whines and hisses light flashes, and the floor shakes.

As the Sidereon’s machinery winds down, a shimmering, prismatic gate opens, and an Emissary from the Plane of Dreams appears: a translucent, opalescent thing like a hybrid of jellyfish and salamander, floating in the air as if drifting in gentle waters. Its head has three faces, each smooth except for a single eye and a flat, expressionless mouth. It speaks telepathically to the characters:

The strange creature’s thoughts fill your head as if you were remembering an old song, heard in your youth and since forgotten. “We are an Emissary from the Realm of Dreams. We come forth from the luminous shadow of the Silver Gate to give you warning, for one passed from here and returned with what she should not have taken, and it is a doom to the worlds, for her dreams, dark and venomous, flowed out from her in our realm as ink from a quill.  She intends to conduct a ritual to resurrect a titan, and she already has the first object she needs to do this."

Vor looks at the thing.  "So mate, Whatcha gonna do 'bout , whaddya say 'er name was?  Ah, roight ye didn'.  Anyho, can ye bes doin' anythin' t' aid us, other than givin' warnin'?"  He looks a bit hopeful. "Ma'haps a noice trinket er four?  Ye knows, sompthin' that'd devastate a evil villain?"

"The Atrophian Orb," Xurxos says.  Between all the sounds, shaking and flashing, Xurxos seems to have entered the room.  "So that's where she got it from. The Magister once spoke of this.  What did he says?  Ah yes: such things as good for the sort of magic only the mad would dare perform – at least if you don’t want to see this poor world more broken than it already is."  

The Emissary vanishes as the Sidereon grinds to a halt.

"So now what do we do?" Xurxos says.  "Chasing her doesn't seem to be working."

"I don't know about you guys, but I think heading upstairs is our first best option." Lia says, more than ready to get away from the machine and the room above this one.

Hallanann will search the room. He's looking for either anything valuable or anything powerful.

Perception: 18

198.   
Perception and Investigation respectively.

Vor will assist Hallanann checking the place out.

“We should probably chase after the woman who took the Atrophian Orb, who’s probably the one causing problems our whole time.” Krusk says. Krusk will also look around for anything useful.

Perception: 16

"Can you tell us more about it -- is there a specific way to use it, or a specific place she might be headed? And is there a way to cut her off?"

You don't find anything else of interest or value int the room. 

"Well, let's see," Xurxos says. "Maghiel stole The Cantos of the Black Phoenix which contains information about rituals for resurrecting a dead titan.  Maghiel may be trying to summon a titan.  In the city of Shelzar, of the Ukrudan Desert, there is an artifact that she may very well need,  There is a hunk of flesh that was once part of the titan Mesos."

“That’s pretty disgusting, but we should probably get there before her and steal it before Maghiel gets to it.” Krusk says, giving up on searching after finding nothing.

"I would think that so long as it continues to exist," Hallanann thinks aloud, "she would continue to come after it. Maybe we should just get there and burn it." To emphasize his point, he creates a small flame in his hand using Prestidigitation then snuffs it out.

(Do any of us have any idea how far away Shelzar is, how long it would take to get there?)

Shelzar is about 1000 miles to the south west.  Here is a map: