Banished

Isabelle!
Lucas!
I got banished., he says with a shit-eating grin on his face.
What...?
The guard behind Isabelle gives her a stern look, the one in front of her turns around:
No chit-chat, move along.
Isabelle takes a moment to understand the implication of what Lucas had said.
...ohhhhh. Congrats!
The guards grab her by the arms and drag her away.
Move!

They bring her to a room adjacent to the main court room where a bunch of important-looking people in suits are waiting for her. They introduce themselves and they all, including herself, sit down around a somewhat large table. One of the suits addresses her:
Before you go to trial, we have something to discuss with you. You are being accused of breaking and entering, property theft, interfering with law enforcement, compromising operationally critical systems, and conspiracy of terrorism. Some of these charges alone will land you in prison for a long time – unless you take this deal...
He grabs few sheets of paper from his briefcase and slides them over.
Basically admit to everything you're accused of and you will be banished instead of going to prison.
She absentmindedly acknowledges what he said as she is already reading the first page.
After reading it, she says: There's a bunch of things in here that aren't true.
Take it or leave it.
What are you getting out of this?
We don't want people like you here. You cause too much trouble.
What will happen if I sign this?
You will be removed from Sunside Cove.
That's what it says. And in practical terms?
Another one of the suits answers: There is an ongoing power outage to parts of the city. We will have to send an expedition outside to fix it. You will join them and not return.
She looks back at the pages.
... Okay...
The other pages are some half filled-out forms. She is given a pen and told to fill in the rest.

something is missing here, maybe add a paragraph about the trial itself

Isabelle is taken to a cell with no bed or toilet, just a bench. She sits down and waits. The guard leaves and the hallway gets quiet. The only thing she hears is the hum of the flourescent lights. She waits some more. Time passes.

The lights go out. Relays click in the hallway. She tries to look around. The streetlight outside the tiny cell window projects a small shimmer onto the ceiling that slowly fades until she is surrounded by complete darkness. It gets even quieter than it was already – not even a noise from outside.

After quite some time, she hears a door open. A guard comes walking down the hallway, looking into all the cells with a flashlight.
He arrives at her holding cell and says: Good afternoon. while opening the door, pointing his flashlight back where he came from.
That way. Someone will be with you shortly.
You're just gonna let me go by myself?
There aren't that many places you could run off to. Now go.
She gets up and does as she is told. The diffuse light reflecting off the floor and the walls lets her barely see her surroundings. Another gaurd appears in the door at the end of the hallway, holding a flashlight as well.

She is cuffed and brought to a car where two other guards are waiting. It's a short ride from the prison to the nearest train station. Apart from a few cars moving around, the entire area is completely dark. No steetlights, no lit-up windows. It is dark enough that she can see a faint shimmer on the dome ceiling, reflecting from other parts of the city.

A train is waiting at the platform. Rather than the usual metro, this one is made up of a battery locomotive and a few flatbed cars. The guard hands the key to her handcuffs over to a guy who seems to be in charge. They sign some paperwork. Then, the guard leaves and the guy tells her to go sit on the last of the flatbed cars.

A few minutes later, the same repeats with Lucas. He sits down next to her and they start quietly chatting.
Any idea who else is gonna join us here?
dialog here

Note: It was always intended that at least some of the rebels who got caught will be released to the outside. However, before starting this chapter, I have never actually considered what this means for the rest of the story. The following chapters weren't originally written with this in mind and may need to be significantly revised to take it into account.