With Peter growing increasingly concerned, Video Walter says Peter will never see him again, because it had to be this way to ensure the future of our humanity. "Your future. The future of Olivia. The future of Etta," he says. Look, are you just going to keep listing humans? Because I think you covered it with "humanity." Video Walter says he doesn't want Peter to be sad: "The time we had together was stolen. I cheated fate to be with you and we shouldn't have had that time together, but we did and I wouldn't change it for the world."
Video Walter says he doesn't want to say goodbye: "But I will say smell ya later." Or "I love you, son." One of the two.
Anyway, Actual Walter tells Peter that he does know what the syringe is for. It's a time travel inoculation and he's taking Michael into the future. He's already been inoculated, but the syringe is a backup in case something happened to him and someone else needed to bring Michael across. Aaand right now we know that someone else is going to be using that syringe.
Peter, eyes wet and Adam's apple bobbing, asks Walter if it has to be this way and an emotional Walter explains that he and Michael will become a paradox. Since nature abhors a paradox, it will heal itself by deleting Michael and him at the moment of the invasion: "The boy and I will disappear after 2015," says Walter. I -- but -- why -- wouldn't -- oh, never mind. Look, it's not like time travel will ever actually be a real thing, so I guess there's not much point complaining about arbitrary paradox rules in the series finale. I should probably just concentrate on how John Noble and Joshua Jackson crush it in this scene, which they do, and I guess that's the main thing.
"So in order to maintain a future without the Observers, you and Michael will have to live out the rest of your lives in the future," says Peter. Walter says in his soul he knows this is what he has to do. He wants Peter to give Olivia their daughter back -- um, I think Olivia is working her ass off here just as much as Peter -- and he wants to give Peter his life back. How could he as a father not do that for him? "You are my favorite thing, Peter. My very favorite thing." They hug and cry, and hug and cry, and -- uh, guys? It's your plan and I don't want to tell you how to set it in motion, but the world isn't going to save itself, you know. Michael continues to silently watch the proceedings.
Astrid and Olivia show up at Apartment 513, apparently to retrieve the trigger from December, but when they get there the door's ajar. They draw their guns and slowly make their way in, spotting a Loyalist's cap and his weapon on the entrance coffee table -- lot of good it does him there -- and then the Loyalists themselves, so Astrid and Olivia duck out of the doorway. And that's when they spot December, hanging from a pipe, his face beaten and bruised. There's also a case with an empty trigger-shaped hole in the foam. Olivia shoots one of the Loyalists and then gets the drop on the other. "What happened to the part?" she asks.