After the final episode, Miles, Charlie, and Monroe are fighting the good fight against the Patriots. Meanwhile, Rachel, Aaron, and Priscilla are doing their own thing in another town...kinda. Rachel is still obessessing over the nanos and so she gets one of the pendants back online to ward them off. Aaron and Priscilla are initially against this because they want to live a normal life. Next thing you know, Grace shows up half dead because she's been trying to find Rachel while being hunted by nanos. In her dying breaths, she gives them a virus that will kill off the nanos.
So with that, the three of them set off to the White House where the other three are, they team up for one last mission and go to the town we saw at the end of season 3. By now, the nanos are welcoming people with promises of laptops, microwaves, electricity, and such at one cost: their humanity. Essentiallly you're in a society where you can't be angry or show any negative emotions. If you've seen the trailer for "We Happy Few" it's like that. Neville lives here and has forgiven the Patriot president for killing Jason (i forgot about that).
Our band of six waltz into the place because the people want them to stay. Aaron and Priscilla set up shop in a house where they try uploading the virus to a computer. Bass, Rachel, and Miles are just outside the door, ready to kill the approaching citizens (lead by Neville who still shows signs of being evil) just as Aaron and Priscilla walk out with Bass' kid pointing a gun to their head. Something happened to make Bass snap and shoot Neville in the head then all hell breaks loose.
The six of them get behind cover while Aaron and Priscilla try uploading the virus....and get turned into swiss cheese in the process. Since there's no time for mourning, The remaining four run to an alley and get ready for a final fight. Rachel isn't having any of that. She says her apologies and says goodbye to everyone. She gives a kiss to Miles and tell him to look after their daughter. (In hindsight I guess I saw this coming, but whatever).
Rachel takes off her pendent and gets possessed by the nanos or something.
That's what's happened so far.