In a nutshell...
Solomon Grundy, who died in last season's The Terror Beyond, is brought back to life (or as much life as a zombie can be brought back to) by a couple of nerdy teenagers messing around with chaos magic. It's worth noting that Grundy died in order to save HawkGirl, Supes, Diana, Dr. Fate, Aquaman -- and basically the world -- from being taken over by an evil alien presence. Although he's definitely considered a villain up until that point, Terror showed a much more sympathetic side to the character as well as his origins, and he and HawkGirl strike up a strange, rather touching friendship there at the end.
In Dr. Fate's towery thing, Aquaman and HawkGirl are playing chess while the android Amazo watches. Aquaman taunt's Shayera's listless attitude towards the game, pointing out that (according to Diana) Shayera used to regularly beat Batman --
(Side note: Shayera and Bats regularly playing chess -- too cute. Need a fic about this. And about Diana finding out. Tee.)
-- and saying all manner of insulting things to try to rile her. Shay won't be riled. In fact, she really doesn't seem to care. Aquaman is frustrated with her attitude. Fate says she still needs to find herself.
Shayera and Fate's wife Inza talk briefly about the state of limbo that she's in: she's been stripped of her rank of Lt. and exiled from her homeworld, and on the other hand "HawkGirl" was just a sham and no one on Earth will ever trust her again. When I do my job, she says, people I care about get hurt. What about when you don't do your job? Inza asks.
Green Lantern, meanwhile, is attending a fashion show. One of the models (Vixen, and I know nothing about the character, suffice it to say she's a black woman with a costume like a Jennifer Lopez dress and the ability to tap into the strengths of animals like jaguars and elephants and things like that) is a member of the League, and when John meets her backstage we find out that they had some kind of date planned. But they're called away because news of Grundy's reanimation has spread.
Back at the tower, Fate, Amazo, Aquaman and Shayera plan to join the conflict, and Shayera points out that he saved them and deserves the benefit of the doubt. Fate retrieves Shayera's mace from the little 'pocket' in reality he put it for safekeeping, and they're off.
The obligatory too-long fight scene ensues. Grundy, and GL and Vixen, trade punches. Grundy's doing a lot better. Superman shows up and also gets his ass handed to him (after offering to 'talk' with Grundy -- what a Boy Scout). Grundy throws Supes into a bridge, which begins to crumble. Aquaman shows up riding a gigantic octopus, which manages to stabilize the bridge. One car plunges over the side and Shayera flies after it, ripping open the top and helping the mother and daughter within to safety.
She turns away from the two and comes face to face (well, face to chest, really) with John.
"Shayera?" he askes, stunned.
She narrows her eyes critically and, a moment later, says "Hate the beard."
So agree, girlfriend.
Fate and the others arrive, and Shayera says she wants to talk to Grundy before they have Amazo teleport him into the sun. But Grundy seems not to recognize her, tossing her aside and returning to mayhem and property damage. Fate says that there is nothing of the old Grundy inside, just a furious monster. Amazo steps in, but freaks out when Grundy starts drawing power from him. Amazon says that they'll be in danger if he stays, that Grundy will keep getting stronger, so he books. Wimp.
More fighting. Fate says that his magic would be useless against the chaos magic that reanimated Grundy. Vixen drops a statue on him, but he finds his way back out and almost tears her in half. Shayera swoops in and takes a whack with the mace, and that seems to do something. She continues at him, hating every moment of it, but the weapon is effective against him. She knocks him straight down through the pavement and into the sewer below, where neither Superman nor GL can see him.
Fate says that Shayera's people's technology, including the mace, was developed to combat magic (which makes sense if you've seen Terror). If there is nothing left of Grundy in that shell, he says, then there's only one thing they can do to help him -- and Shay is the only one who can grant him peace. She agonizes over this, feeling that she is being asked to betray another friend, to destroy another life, and tells a confused John, "Your favorite movie's Old Yeller, you know exactly what he's saying" (continuity from In Blackest Night, IIRC).
John touches her arm. You don't need to do this, he says. Give me the mace, and I'll do it for you.
Cue put-upon look from Vixen.
But Shayera tells him she has to do it herself, because he was her friend and it's her responsibility. She flies down into the sewer and finds Grundy slumped in a corner, groggy and out of it, and tells him to close his eyes. He does so, and she raises the mace over her head...
On the street above, John is pacing while Vixen looks increasingly pissed. Just as Superman is getting ready to go in after her, Shayera flies out. "It's over," she says sadly, then walks away.
A crowd of rubberneckers and reporters has gathered. As Shayera walks away, they snap pictures and call out to her. One reporter asks "Do you think today's actions can possibly make up for your complicity in the Thanagarian invasion of Earth?" Another: "Do you have a comment on your dismissal from the Justice League?"
John steps up. "HawkGirl was never dismissed from the Justice League. She can come back whenever she likes." She's shocked, and he tells her that he reclused himself (because of... ya know...) and that Superman's vote broke the tie (more on this later). Superman says that he believes in redemption and second chances... and his friends.
Idiots shout "traitor!" and "go back where you came from!" and John yells back and them: "Back off! She doesn't have to take that from you people!" Shayera says that no, she does; she somewhat deserves it. She walks away, but is stopped by the mother and daughter she saved earlier. "God bless you," says the mother (and calls Shayera something I couldn't quite make out... but the woman seems to have a Hispanic accent and it sounded like "chica" something, so I'm guessing it's a kind of Spanish approximation of HawkGirl?)
"You deserve that, too," says John.
They smile at each other, and the group walks away into the rising sun.
1. John dating Vixen. Interesting, to say the least. Obviously the debacle in Starcrossed didn't put into place any rules against League members dating. This is good to remember. I started out annoyed with Vixen just for being 'the other woman', but by the end you kind of feel sorry for her. They make it pretty clear that she's ticked off with John's attitude towards Shayera, and is hurt by that, and even refers to her as "pretty Polly". Okay, maybe I didn't feel that sorry for her.
2. The Vote, with a capital V. At the end of Starcrossed part 3, the JL voted on whether or not Shayera should remain a member. However, she decided to resign before they could tell her the results. Now, he says here that he reclused himself, which I think I even predicted in a fic of mine, and that Superman broke the tie. Going by the attitudes in the room in that episode, both Flash and J'onn seemed the most forgiving towards aShay's actions. Both Diana and Superman appeared pissed. Batman, hard to say. So I was surprised to hear that Supes was the one to break the tie in Shayera's favor. On the other hand, the fact that Diana and (we have to assume) Batman voted in favor of chucking her out of the League also has interesting implications. Of course, with JLU's dumbass new format, who knows the next time we'll see Shayera in a scene with either of those two. We're likely going to go the whole season without Flash getting a word in edgewise. Poor fella.
3. I just have to say it again. HG and Bats playing chess. Mwah.
Obviously we're not going to get any followup on this this season, because the two part season finale seems Batman-centered. I can't complain about that. Nor can I complain about Bruce the cowboy (raaow). But unless the writers decide to throw us a bone next season, working out the kinks from the end of this episode will be the fic writers' job. Did Shayera actually kill Grundy (we don't see the death blow. Of course this is a cartoon)? When it comes to John, does Vixen put up a fight? Are there problems reintegrating Shay into the *sarcasm* new and improved */sarcasm* JL? Where does John and Shayera's relationship go from here? Will she be an active member of the League again? If so, she'll be fighting under her own name, without a secret identity or even public persona like Diana has with the 'Wonder Woman' title.
Start writing, people.