Once Upon a Time, on ABC
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I suppose I should mention that at the end of last season, Henry became the new Author. (He broke the magic pen, but later this season we'll learn that's not the end of that.) The biggest thing that happened at the end of last season was that the Apprentice removed the Darkness from Rumple (who remains comatose at the start of this season). The Apprentice tried to trap the Darkness in the Sorcerer's hat, but it escaped and mortally wounded the Apprentice. Before he died, the Apprentice told everyone that the only one who could stop the Darkness was the Sorcerer... aka Merlin. Later, the Darkness took a new host: Emma. (However, she disappeared, leaving behind only the Dagger.)
When season five begins, we see a flashback to Arthur pulling Excalibur from the stone. (He's an adult at the time, unlike in Disney's The Sword in the Stone.) However, he discovers that the tip of the sword is missing. Apparently at some point, it had been broken and the tip was made into the Dagger of the Dark One. Meanwhile, in Storybrooke, Regina uses the Apprentice's wand to open a portal to the Enchanted Forest. (Well, actually, Zelena used the wand to open a portal to Oz, in the form of a twister, but Regina redirected it, and it transports Granny's diner to the Forest.) Before they get there, Emma is wandering around the Enchanted Forest, and she has visions of the Darkness within her, which manifests in the form of Rumplestiltskin. (This reminds me of the Scorpius clone from Farscape.) He (or it) knows things that could be useful to her, but he wants her to embrace the darkness, which she prefers to fight. She eventually meets Merida (from Brave), who is searching for her brothers. The two of them team up briefly, but Emma eventually betrays her, and only refrains from killing her when her friends from Storybrooke show up, and Merida leaves to continue her search. Soon after that, Emma and the others meet King Arthur, who takes them to Camelot. (This is five years after he first obtained Excalibur.) The season premiere ends with everyone finding themselves back in Storybrooke. Six weeks have passed since they entered Camelot, but they don't remember anything about their time there. So from this point on, we'll see flashbacks to that missing time, interspersed with scenes in the present. The biggest mystery is the fact that Emma has now fully embraced her role as the Dark One. (She knows what happened in Camelot, but isn't telling anyone.) Oh, and it's not just the people from Storybrooke who have returned there, but also pretty much everyone who lived in Camelot. And Merida.
In flashbacks, we'll see Henry befriend a girl from Camelot named Violet (a potential love interest), and in the present the two of them also begin a friendship in Storybrooke. Also in Camelot, our heroes learned that Merlin had been transformed into a tree, apparently before he ever met Arthur and prophesied him becoming king. Now Emma and Regina have to figure out a way to free him from that curse. Meanwhile, Mary Margaret receives a warning from Lancelot (whom they'd met in past seasons, but was supposedly dead). He says that Arthur can't be trusted, and eventually we learn that he's right. Arthur wants to obtain the Dagger, so he can make Excalibur whole again, but... eh, he's kind of... I don't even know what to say about all this. He's become obsessed, or whatever, and he's willing to betray anyone to get what he wants, though I can't really remember why it's such a bad thing, since I don't think what he wants really conflicts with what everyone else wants. Still... he's dangerous. And his wife, Guinevere, is dangerous as well, but that's because he'd cast a spell on her to make him obey her. Anyway, Emma and Regina eventually free Merlin, but I guess Arthur wants to kill him. Also, in a side story, Belle and Merida team up to find Merida's brothers and free them from their captors. After that, Merida is crowned queen of Dunbroch. (Her father, the king, had been killed in an earlier battle, though I'm not sure why her mother can't just rule, but... this isn't her story, it's Merida's. So whatevs, I guess.) We'll also learn that Merida received some combat training from Mulan. And we learn who killed Merida's father. Other flashbacks reveal how Merlin gained his powers thousands of years ago, and created Excalibur. And later fell in love with a woman named Nimue. And how her destiny involves the original Dark One, and the breaking of Excalibur and creation of the Dagger.
In Storybrooke, Emma has the Sword in the Stone, but she needs someone to pull it out for her. (It will be awhile before it's revealed how Excalibur got back into the stone.) And she wants Rumple to do it. She wakes him from his coma and kidnaps him. But now that he's no longer the Dark One, he's reverted to his original cowardly ways, and he has to be a hero to draw the sword. So Emma forces Merida to train him to be brave. (Ha... movie pun.) This plan succeeds, and Rumple pulls the sword from the stone and gives it to Emma, though he vows to stop her from doing... whatever it is she plans to do. (Though nothing comes of that promise.) Also, somehow Zelena's pregnancy gets fast-forwarded, and she gives birth to a girl. (The baby is delivered by Dr. Whale, whom we rarely see on the show. It's kind of funny because his hair looks like it does on David Anders's other show, iZombie, and his personality in this episode seems more like his character on that show than like Dr. Whale.) Robin and Regina intend to raise the baby themselves, but also to give Zelena strictly monitored visitation rights. And... we eventually learn how everyone returned to Storybrooke, and what Emma's plan is. Naturally, things don't end up going according to her plan. I don't want to reveal all the details, but I must say it's all about Hook. In the midseason finale, the Darkness is finally (apparently) eliminated, and Emma returns to normal, but at a terrible price: Hook dies. Meanwhile, Zelena wants to raise her baby herself, without Robin and Regina, so Regina uses the Apprentice's wand to summon another twister, and send Zelena back to Oz. Also, Belle decides she wants to get back together with Rumple. However, Emma learns a shocking secret about Rumple (he has once again become the Dark One), which she uses to blackmail him into taking her (and some of the other heroes) to the Underworld, to find Hook and bring him back.
So, in the season's second story arc, Emma, Rumple, Snow, Charming, Regina, Henry, and Robin Hood all go to the Underworld. The place looks like Storybrooke, except the clock tower is broken, and the sky is always overcast, and plants don't grow there. (Incidentally, there was a Blind Witch in one episode of season one, played by Emma Caulfield. This season she has a minor recurring role, running the Underworld version of Granny's diner.) The main antagonist for this arc is Hades (from Hercules; he's played by Greg Germann, and occasionally has CGI blue flaming hair, though not all the time). Throughout the arc, our heroes will also meet various people from their past who have died (some whom we've seen before on the show, and some we haven't; in one episode, we learn that when Snow was young, she'd met Hercules). Anyway, they discover that any souls in the Underworld have unfinished business that prevents them from moving on (so I guess it's basically Purgatory). They can stay there forever, or they can end up going to a better place or a worse place (presumably Heaven or Hell, though we don't really get to see either destination, and it could be different versions of such places, depending on each individual's culture, I imagine). Of course, in addition to looking for Hook, the heroes decide to try to help various souls finish their unfinished business, so they can move on. This really pisses Hades off, so he tries to make sure none of the heroes will be able to leave the Underworld themselves, even once they find and rescue Hook. Which means that after they do rescue him, they have to try to figure out how to defeat Hades, so they can return to the real Storybrooke.
We also learn that when Henry broke the Author's pen, it ended up in the Underworld. He eventually finds it, and accepts his role as the Author. Cruella wants to get him to write her back to life, but he doesn't do that. (Oh yeah, I didn't tell you this before: in season 4, Emma killed Cruella.) Unlike Isaac, Henry is going to do the job right, which means only recording what happens, rather than using his power to control events. Also in this arc, we learn that Belle is pregnant with Rumple's child... which is a problem, because in a flashback to before he originally became the Dark One, we learn Rumple once made a deal granting his second child to a magical healer named Fendrake (played by Aaron Douglas, whom I knew from Battlestar Galactica), in order to save Baelfire's life. He didn't intend to ever have a second child, but now he will. And Hades has obtained the contract from Fendrake. So now Rumple has to find a way to stop him from taking their unborn baby. Oh, and Belle ends up in the Underworld, along with Zelena and her baby, but I don't want to try to explain how that happened. But Belle eventually puts herself under a sleeping spell, to ensure Hades wouldn't speed up her pregnancy, as Dark Emma previously did to Zelena. She does this to give Rumple more time to find a way to stop Hades. Meanwhile, more flashbacks reveal that Zelena and Hades have a past together; in fact, they are in love. But... that's all really complicated. Meanwhile, our heroes find Ruby is in the Underworld, looking for Zelena. In flashbacks, we find that Ruby and Mulan had met Dorothy Gale in Oz, and later Zelena put Dorothy under a sleeping curse. Eventually, Ruby and Snow both go to Oz, where Ruby manages to wake Dorothy up. Then Snow goes back to Storybrooke, to be with baby Neal.
Oh, and there's something about Zelena I don't think I've mentioned before, even though it was revealed back in season 3: she's actually Regina's sister, and Cora had given her up as a baby. So Zelena has long resented both her mother and her sister. But Cora eventually reveals something to her daughters that patches up the sisters' relationship, which was Cora's unfinished business, so she finally moves on. And Regina, who originally wanted to convince Zelena to give up on a relationship with Hades, now encourages her to pursue it, in hopes of changing his villainous ways. But Zelena ends up being kidnapped by Peter Pan, whom Rumple had killed in season three, but who is now working with Rumple. (Oh, and I probably never mentioned this before, either: Pan is actually Rumple's father. I know, right?) Anyway, the heroes eventually get Zelena back, and Rumple betrays Pan. And later, everyone except Hook manages to return to the land of the living. Hades also goes to the real Storybrooke, along with Zelena. (Now that Hades is gone, Cruella decides to take over the Underworld.) Soon after arriving, Hades kills King Arthur, who winds up in the Underworld and goes on a quest with Hook to find something that will help Emma defeat Hades in the real world. But not before Hades kills Robin Hood, using something called the Olympian Crystal, when Robin gets between Hades and Regina, whom he was really trying to kill. (Actually, "kill" isn't the right word, because the Crystal apparently destroys a person's soul, so there will be no afterlife, and no chance of returning or moving on.) So, Zelena finally realizes Hades hasn't changed, and she destroys him with the Crystal. Meanwhile, the help Hook had provided to the heroes allows him to move on, while Arthur stays in the Underworld to try to fix that "broken kingdom." And after Robin Hood's funeral, Zelena decides to name her daughter Robin. Later, Rumple acquires a piece of the Crystal, which everyone else thought had been destroyed along with Hades.
Also after the funeral, Hook is returned to life and sent back to Storybrooke by Zeus, as a reward for helping defeat Hades. Emma is overjoyed, but concerned that the unfairness of her getting her love back when Regina will never get hers could lead to Regina turning evil again. This doesn't happen, but Regina confides in Emma about her constant struggle to keep the Evil Queen in check. Meanwhile, Henry and Violet take a road trip to New York, to search for a way to destroy magic, which he believes has caused his family nothing but pain. (Violet is on board with this, because her mother had been killed by magic.) He knows his father, Neal, had been searching for the same thing, and follows up on that, eventually discovering a Dark Grail (the opposite of the Holy Grail, which had been the origin of all magic). Regina and Emma try to find Henry and stop him, in part because Rumple had implied that destroying magic would destroy Storybrooke. So Zelena opens a portal to let all the citizens of the town return to their proper realms before that happens. But Zelena, Charming, Snow, and Hook are all somehow transported to a previously unseen realm, the Land of Untold Stories, where they are taken prisoner by someone called the Warden. They receive some help from a groundskeeper, a former doctor who had been subjugated by the Warden, and who wants the heroes to take him with them when they return to Storybrooke. But it soon turns out that he is actually Dr. Jekyll, and the "Warden" is Mr. Hyde. Jekyll creates a serum that separates the two personae into separate bodies. Meanwhile, in New York, Regina and Emma find Henry and Violet, but they don't stop Henry from destroying magic. Rumple had also gone to New York, to retrieve the Crystal, which Henry had stolen from him. He planned to use its power to revive Belle, but she ends up being taken through a portal by Hyde. When he learns where she is, but that it would be impossible to retrieve her after Henry destroyed magic, he takes the others to the Dragon (who had been seen in one episode of season two), who still has some magic. Not enough to open a portal to the Land of Untold Stories, but he does say some things that inspire Henry to find more magic, with help from Regina, Emma, Rumple, Violet, and others (though the way he convinced those "others" to help was massively improbable). They manage to bring their friends back, along with Jekyll, as well as restoring the magic that Henry had destroyed. Meanwhile, Rumple goes to the other realm and makes a deal with Hyde, who has information on a way to revive Belle (which I expect will happen next season). Later we learn that Jekyll still had some of his serum, which Regina uses on herself, to rid herself of the Evil Queen. After her dark side emerges, Regina kills the Queen.
In the end, Hyde goes to Storybrooke, along with any number of other characters from his realm. (Oh yeah, the town hadn't been destroyed by the temporary loss of magic. That was just a bluff on Rumple's part.) And Hyde says that Rumple (or Mr. Gold) had given him ownership of Storybrooke. (I don't think the point of Gold owning the town had been mentioned since early in season one.) Also, it turns out the Evil Queen hadn't been killed, after all, even though Regina had crushed her heart. She appears in the Dragon's shop and takes his heart, though as yet it's unclear what she means to do with it. In any event, it looks like she and Hyde will both be major antagonists in season six, and lots of other characters are likely to be introduced. So it should be pretty epic, and I greatly look forward to that. Meanwhile, I want to say I found the parallel between Jekyll & Hyde and Regina & the Evil Queen pretty neat (and I guessed early on how that would play out, except for the part about the Evil Queen surviving). Another thing I liked about the finale was that Violet and her father, Sir Morgan, don't return to Camelot. It's revealed that Morgan was actually "a Connecticut Yankee" (from Mark Twain's story), so while I guess they'll be going to Connecticut rather than staying in Storybrooke, at least Violet and Henry won't be in different realms. (At least I don't think they'll stay in Storybrooke. I could be wrong. Certainly I hope to see more of her in the future, and I hope the writers do a better job of developing her character. Because I never really felt like they did enough with her, this season, never made her much more than "a girl Henry likes." She deserves to have a more fully realized personality.)