This article contains spoilers for the Supergirl season three episode 'Wake Up'.
The Supergirl episode 'Wake Up' did not have a villain of the week or any real battles at all. It was an episode about reveals and, well, people waking up. It also sets up what is likely to be some of the biggest stories for the rest of the season.
The main story is that the alien ship under National City is found by a submarine assessing damage after the attack in episode one. The alien ship defends itself and wakes up one of the occupants inside. Kara, Winn and J'onn J'onzz go to investigate and discover a handful of humanoids in stasis chambers, and they open one. The person opens fire on Kara before realizing who she is… and we see that it's Mon-El.
He doesn't explain anything and looks exhausted, waiting for his chance to steal an energy source — but is caught by Kara. He convinces Winn to help him out, and we learn that while it's been seven months since he went into the wormhole, for him it's been seven years. He's been living in the 31st century. With the power on, they're able to keep the pods going… except for one that Kara has to smash open, and Imra Ardeen is revealed. Imra is also Saturn Girl and, we find out, Mon-El's wife. That's probably going to cause an issue or two.
The second storyline involves Samantha Arias going back to see her adopted mother, Patricia, and trying to find out why she has superpowers. Though they have a very strained relationship, Patricia finally shows Sam the truth. And we get an origin almost straight out of Superman, with the alien ship in the barn, given a command crystal, etc. She heads out to the middle of the desert where no one is around… and the rocks begin to shift in big ways, creating her Fortress of Solitude. She puts the crystal in place and learns that she is an instrument of extreme justice: a Worldkiller. And where the birth of her daughter delayed he awakening, she was now being switched on… and the Sam we knew seems to be gone. Heavy emphasis on the "seems."
The third story here is between J'onn and his father M'yrnn, who appears to have been "holding it in" for four weeks and finally asks for the bathroom. Winn and Alex push J'onn to take his dad out into the city; show him the world. J'onn does, but still is tied to the office, which is the center of his life. M'yrnn points that out and J'onn ends up realizing that with no family, he has made his job everything. He lives at the DEO. But he's not alone anymore. He finds an apartment and offers to move into it with his father, so they can make it their home. If M'gann ever returns and moves in with J'onn, you'd have the makings of a great sitcom.
This episode changes a lot of things. Kara goes from mourning the loss of Mon-El to having to deal with him being with another woman. Sam is now switched on, but to what extent? Will she still try to be Sam, or is destruction her full-time job now? Why have Mon-El and Saturn Girl come back to this time? How long have they been under there (a long time, according to Winn), and are they there to stop Reign? Is Reign the only Worldkiller, or will there be others like in the comics? And what might be the most fun question: who is in the other pods? Six total, which leaves four unopened. They announced casting of Brainiac 5, so he is likely one. What other Legion of Super-Heroes characters will we meet this season?
Next week, it looks like the ongoing storylines are put aside (maybe) as Kara and Alex head to Earth-1 for Barry Allen and Iris West's wedding. The wedding is invaded by Nazis from Earth-X, and the Arrowverse crossover event kicks off. Unlike last year where the crossover started in the last five minutes of Supergirl before moving on to The Flash, this will envelop all four shows completely and seem like a single four-hour show instead of an episode of each individually. And Arrow will be moving to Monday next week at 9 p.m. ET, so there will be two hours that night and two hours the next. You had to know they'd get around to doing a Crisis story sooner rather than later.