Why did the lights aka power go out? What did Rachel have do with that?
Her knowledge of this, not to mention her involvement in it, has been hinted at for months. And tonight we find out the story. "Nanites" which could keep Danny healthy - remember we saw how sick he was prior to the blackout - can't work in our plugged-in and digital world. So Rachel and colleagues made it that all go away.
Danny lived, the world went dark and on the verge of barbarism, but that was ok, as long as Danny lived. His death a few episodes ago did more than traumatized Rachel - it showed her that the world she had helped bring into to being, to save her son, had killed him anyway. That's why she's so determined now to turn the lights back on.
A pretty good story, and satisfyingly logical as science fiction, too. Because of that, I'd say Revolution is now one of J. J. Abrams' best franchises.
Meanwhile, there's good other stuff going down too - down, that is, in the old South, in the new Georgia Republic which is far more than our current state of Georgia, though Atlanta is still its capital. There Miles not only stops a nuke from Monroe, but makes an alliance with Georgia's leader, played by Jack Bauer's late wife Teri (played by Leslie Hope) on 24. Should be some big times ahead as Miles agrees to "become a general again," and lead a sizable troop of solders back to attack his power-crazy former partner from the inside-out.
See also Revolution: Preview Review ... Revolution 1.2: Fast Changes