I know that this is dead. I'm not trying the revive it.
It's just that the story won't leave my head.

So I'm putting the basic plot line here, for you all to read.

All of the mystery, all of my plans. They'll be revealed. My decisions, explained.

First, I should explain the general plan of that last chapter:
- The two teams would've met in an abandoned underground garage.
- The Foundation was seeking to recover SCP-2693-C. The GOI, to prevent that.
- The computer would've been at the lowest floor of the garage.
- The floors would've been almost maze-like; tarps were put up the create rooms and make it difficult to find a way to the computer.
- O5-6 would've ordered that they split up to cover more ground.
- This is where the fighting would start.
- They'd find the computer, but the Leader would kidnap Six.

The chapter would end with Six being knocked out and restrained in the possession of the GOI. There'd be a post-it on her face that would have the explicit orders from the Leader to not kill her.
The Foundation would be none the wiser; the Leader would've taken Six's place.

Next chapter would start with a noticeable difference in the attitudes of all the O5s. 'Six', obviously, would only have a difference in general expressiveness.
But the others?
They'd be locked in their respective offices, horrified of what 'Six' told them.
'Six' would tell the Foundation characters that it was found that the Chaos Insurgency was working with the GOI. So, a counterstrike was ordered. They were going to dismantle the Insurgency by killing its leaders.

While that was going on, the GOI would have some time to talk to Six. They'd still be under the orders to not kill her, and she'd be furious at their mutiny.
Some arguments may start, but that'd be interrupted by an audio message from the Leader. As always, it'd end with 'harden your hearts'.
Six would react to this statement, but refuse to say anything.
Their new orders? Release SCP-682, who had strangely willingly returned to containment, on the Global Occult Coolition headquarters.
Perhaps most importantly, they were meant to wear Foundation uniforms while doing so. And anomalously force Six to be the one that unleashed 682.

The attack on the Insurgency would be successful. Upon returning to Site-01, the group would learn two things:
1. A group of Foundation personnel, lead by a redacted Overseer member, used SCP-682 as a weapon against the GOC.
2. There would be a memo directed to all members of the Foundation in a few weeks.

Next chapter, research time. The Foundation group, without Six's knowledge (after all, she could've been one of the ones to order the attack on the Foundation's greatest ally), would do anything they could to learn about the attack.
And, well, they'd have some help from the Ethics Committee, who had decided that the Council needed to be stopped before the memo's release.
With the Committee Head's help, the group would finally find a video.
O5-6 would be pictured opening the portable containment that held SCP-682. While her movements wouldn't be robotic, if they zoomed in on her face they'd see that her eyes were blank.
The video's timestamp would be the same date and time that the group was attacking the Chaos Insurgency.
Before they could absorb this information, however, 'Six' would call the group to action.
They would have to recontain 173.

Meanwhile, Six would be getting a little confident. First, she would try to squeeze information out of the GOI characters. When that failed, she'd demand that they kill her. Even try to goad them into it.
Obviously, that would be another failure. So Six would have to use her trump card, and mention that she knows why the 'Leader' may want her alive.
This is where the two big mysteries would be solved.
1) Six's anomalous property: When Six dies, a large-scale antimemetic effect would be triggered. She'd be erased from history and memory.
2) The Leader wants to prevent this. After all, the Leader is another Six, originating from the universe of SCP-5000.
After reacting appropriately, Six would mention that the Leader's goal was probably to end humanity, just like it had been in the universe SCP-5000 came from.

This is where the chapter would end.
I hadn't figured out how the rest of the plot would go. But now I have it in writing, so this may hopefully leave my head once and for all.
I hope you all enjoyed this roleplay. It's definitely the one I put the most thought in, so it's a shame that it had to end this way.