The one who spoke to Harry. Do you think that person is who they keep trying to get to? Nemesis controlled Maeve tried, He Who Walk Before tried, Nemesis controlled Justine tried. Then there is the whole Rashid focusing the Tank at some point and it involving Demon Reach....
Originally I thought the Outsiders were trying to break someone out. That may be the case but now I'm wondering if they want that prisoner, and not to break them out. Maybe to kill him, or to get information from him....
Remember what he said? "I need to be here". Maybe he isn't a prisoner at all. Maybe he's there kind of like Thomas. Locked up for another purpose. To preserve him, or protect him or something like that. I'm wondering if he needs to be there until the Stars and Stones. He will play a role, but other forces want to stop that from happening.