With 13 — now only 12 — episodes left to wrap, “Games of Thrones” is officially in the business of speed. Speed means efficiency, and efficiency means cutting waste. Without making this final lap look as if McKinsey & Co. has come in with its own plan for streamlining Westeros’ last stand, “GoT” does need to make every word, every glance, every scene count. Sunday’s 7th season opener, “Dragonstone” — really with the exception of the crowd-pleaser opening scene — was indeed a marvel of economy. Much ground was covered, no time wasted — yours above all.

So, here’s a quick look at some of the key scenes, and what they may tell us about the next 12, beginning with . . .

The return of Walder Frey (David Bradley): Because we know Arya (Maisie Williams) learned well at the House of Black and White, and at the tutelage of Jaqen H’ghar (Tom Wlaschiha), we know she has no immediate plans to forget her lessons. Most fans almost certainly saw through her most recent guise, and knew exactly what she had put in that finest of wines. Consider this the official end of the Red Wedding saga. Revenge has been served along with the wine. She can now move on. But what’s so interesting about this scene wasn’t the scene itself, but what it says about the future. Arya’s shape-shifting gift is all but undetectable. Recall what she tells her new friends during her travels — she plans to “kill the queen.” They laugh. She laughs. The queen won’t laugh. Arya has a killer app. Literally. She can shapeshift into anyone, even the queen.

The March of the White Walkers: Out there, in the cold, beyond the Wall, they are moving. The best part of this scene was of course arguably the best scene of the night. The wildling’s much-beloved giants who were killed in the recent troubles have returned as wights. It reminded me of Boromir’s classic line from “The Lord of the Rings” in the mines of Moria: “They have a cave troll.” The Walkers have something even better.

Jon and Sansa: Team Stark is now ruling the north, or at least one half is ruling the north. Jon (Kit Harington) needed to establish his authority as King of the North, but the opening act obviously suggested that “uneasy is the head that wears the crown” — especially when he’s got a smarter partner. Sansa (Sophie Turner) is not technically the “King’s Hand” — which would mean that she would offer her counsel in private as opposed to offering it in that especially public forum.

The squabble between her and Jon — whether to reward the Umbers and Karstarks or to punish them – might seem academic to us, but to the future of the north, of Westeros itself, it is pivotal. By punishing those who were traitors (Sansa’s position), she’s taking a traditionalist approach. Take away their castles! That’ll teach ‘em! Jon sees it otherwise. His coalition is built on pragmatism. They may have been on the wrong side of the battle of the bastards, but we can hardly blame them for following their leaders orders, he essentially says. Those leaders are dead, so he proclaims both houses effectively absolved of their sins. The kids are told to pledge loyalty, and they do — about as perfunctorily as if told by the teacher to put away their books.

So who’s right, wrong? Sansa is right if the past is the guide. This is how traitors are treated, and surely those in the room here at Winterfell cannot be fully trusted. Jon, meanwhile, is about the future. But here’s the problem with his position — he’s handed the keys of the car over to the children, and at what point will they be manipulated by the adults? This new allegiance doesn’t feel quite as pragmatic as it appeared. Advantage Sansa. She’s right. Reward your friends, punish your enemies — who will come around eventually anyway.

Jon handles his first major executive decision petulantly and for everyone to see. His new allies now know a.) He’s not totally in control, and b.) He has a smarter consigliere named Sansa, c.) They got away scott-free. That’s why Littlefinger (Aiden Gillen) smiled his wicked little smile at the end of this scene. He knows Jon’s hold is tenuous.

Cersei and Jamie, reunited: In terms of pure economy, this is the best scene of the night. We learn mostly that Cersei (Lena Headey) has lost her mind. She is now officially a tragic figure as opposed to a triumphant one. Her victory over the Sparrows means nothing, her ascendance less. Jaime (Nikolaj Coster-Waldau) sees in her a lost soul — someone without bearings, even as she stands on the map she has memorized. Nothing at her feet is stable, the future less so .. enemies to the east, west, south, north, etc. There’s one more enemy — the one within.

In the scheme of “GoT,” Cersei remains a complicated figure. Sansa (earlier in the episode) is not wrong — that she’s murdered everyone who ever stood in her way — but she’s not entirely right about Cersei either. She’s a woman who has had to fight the same battle that Dany has had to fight: Both are consumed with destiny, both must also contend with an entrenched patriarchy that’s consumed with its own destiny. Both are ruthless, but we’ve come to see Dany’s actions as heroic, Cersei’s as monstrous. She and Dany really are just one and the same. Dany just doesn’t know it yet.

Euron Greyjoy makes a proposal: This is a fascinating scene because of the last line Euron (Pilou Asbaek) tosses to Cersei, “the surest way (to gain trust) is with a priceless gift and I won’t return until I have that for you.” What priceless gift would make her want to marry this creep? What could be “priceless” to Cersei at this point? Well, obviously Dany’s head but she’s going to be denied that. More allies would be nice, but most of those seem otherwise engaged. To Euron, “priceless” may mean a different thing altogether — perhaps someone who won’t challenge Cersei’s hegemony, or future, or throne.

I’m liking the idea of that “gift” as Gendry Baratheon (Joe Dempsie). Gendry is last of the Baratheons and was set adrift in a rowboat by Davos a couple of seasons ago. If Euron has captured Baratheon — which shouldn’t have been too much trouble — then he could present him to Cersei, who might see him as a potential ally.

Here’s how that might play out: As the last of the Baratheons, Gendry might be able to muster those forces who were loyal to Stannis who still believe a Baratheon should be on the Iron Throne. Her son Tommen, now deceased, was also a Baratheon and served roughly the same purpose. Of course you’d have to ask why Gendry would want to comply.

There is another possible gift: The Red Woman, who would make an interesting Cersei ally as well. She was banished by Jon last season, so has no loyalty to him. Her loyalty was with the Baratheons, but they are all gone. Why not throw in with Cersei? The problem (among many) with this theory: Euron has boats, and the last time we say the Red Woman, she was on a horse.

Ed Sheeran comes to Westeros: Wouldn’t you know that the one scene that was almost a complete throwaway -- the one we didn’t really need -- was the one starring Ed Sheeran as troubador and wandering minstrel, who offers Arya a leg of rabbit and a song, but who offers us nothing much of anything else. He was with a group of other wandering soldiers, who weren’t much interested in war as much as having a good time. It was also probably the most-discussed, most-tweeted scene of the night. Why Sheeran here -- he was expected but not this early in the season? Musician cameos are certainly nothing new on “GoT:” Dr. Feelgood, Mastodon, Molotov Jukebox, Of Monsters and Men, Snow Patrol... But these certainly aren’t on quite the same level, famewise, as the musician last night. We could surmise that he’s a superfan or that Masie Williams might be a superfan, too. (Both). Anyway, it was pleasant scene and potentially an organic one, if he returns in a pivotal future scene. (Let’s hope). At the very least, this scene did offer one of the best lines of the night -- Arya on why she’s going to Kings Landing: “... to kill the Queen ...”

Samwell does the dishes: Another great scene, whereby poor Samwell (John Bradley-West) must clean out the (umm) urinal pots. (Ah, so this is how one becomes a maester? Lovely . . .) The books in the library are behind chains, literally, and their knowledge effectively unattainable. But Sam comes from the real world, those in the Citadel live in the past. Sam has seen the Whitewalkers, but the Grand Maester — Jim Broadbent makes his entrance — doesn’t really care. “We are the world’s memory. Without us, we would be little better than dogs.” History has proven, he says, that what seems like the end is only the beginning of something else, while “The wall has stood through it all and every winter that ever came has ended.” We are now predisposed to believe that the Grand Maester is another fool or oblivious. But I think Sam will work on him. This Grand Maester will prove a valuable ally yet.

The return of Clegane and Beric Dondarrion: This is my favorite scene, and I think the most important of the night. Clegane (Rory McCann) and Beric (Richard Dormer) of Brotherhood of the Banner — who had earlier killed — are wandering in the darkness when they come to the abandoned house. Clegane — the Hound — is in a foul mood wants to know why the Lord of Light keeps bringing you back?” (Dondarrion has been killed six times, twice by the Hound.) “I only know he (the Lord of Light) wants me alive.” Clegane is later told to look in the fire, where he sees the army of White Walkers, then Beric tells him that now “you know we are here for a reason.” What’s especially interesting here however is Beric’s question: Why? Beric’s revival predates Jon’s, and to an extent might foreshadow Jon’s fate. To come back from the dead here doesn’t really mean ever being fully alive, but merely in a state of decline. From the dead he came, and to the dead he will return. Beric is a wight-to-be. The question then has to be, what role will Clegane play in the future? He has an uncertain ally in Beric. We know that much, but he has no idea how much just yet.

Sam discovers the big secret: The books in the Citadel’s library finally yield a valuable secret. Readers of “A Song of Ice and Fire” know that there’s a mountain of dragonglass on Dragonstone (Dragonglass is the only thing that can kill the Whitewalkers) and now viewers of a “Game of Thrones” do, too. A mountain of it is beneath the ground, and this is news he must get to Jon.

Ergo: J + D =? Jon will now have a pretty good reason to meet Dany, who returned to her birthplace Sunday night. There they will learn that they are related (she’s his aunt) perhaps. She will also learn that there’s a bigger problem than Cersei to contend with.

(Oh, and that hand, covered in grayscale: Jorah Mormont (Iain Glen). I had no idea he was imprisoned in Oldtown. The big question: Why is he here?)

Dany returns to Dragonstone: Of course, this is huge. Daenerys Targaryen (Emilia Clarke) returns to her birthplace, Dragonstone, where she will launch the final conquest of Westeros. It’s a beautiful scene, powerfully established. Every shot in this is a keeper. Scale is of importance here: Everywhere she goes, something vastly larger than her looms. The throne room itself is this vaunted soaring space, the throne a jagged sharp tooth. You can read this place a couple of ways: It’s testament to the folly of ambition, the folly of kings or perhaps queens; or, is a place of unfinished business, waiting . . . waiting for someone to complete whatever it existed for in the first place.

“Shall we begin,” she says. We shall, Dany, we shall.