We saw a ton of Avengers: Age of Ultron footage, which starts light-hearted. We see the Avengers sitting around trying to untangle the “whosoever is worthy” thing, regarding who gets to hold Thor’s hammer. And they all think it’s a trick, or a circus sideshow.
"If I lift it, do I get to rule Asgard?" Tony asks. And Thor says yes. Tony says he will be fair but firm, and maybe work out the "wench clause." Tony can’t lift it — even after he puts on an Iron Man glove and gets Rhodey to help him. Soon everybody is trying to lift it — including Bruce Banner, who gets kinda upset — and only Steve Rogers even comes close.
Black Widow doesn’t even want to try lifting it, because “That’s not a question I need answering.”
Tony guess it’s keyed to Thor’s finger prints, or some other biometric, but Thor says the answer is simpler: “You’re all not worthy.”
Then there’s a ringing sound and they’re all deafened, and Ultron strides into the room, with a crude Avengers logo painted on his slightly misshapen chest. “How could you be worthy? You’re all killers,” Ultron says. “You want to protect the world, but you don’t want to it to change. There’s only one path to peace: your extinction.”
Then a shit ton of robots burst through the wall and attack all of the Avengers, plus Maria Hill.
Then we hear Ultron’s voiceover saying he had a vision of the whole world screaming for mercy, and everybody tangled in it.
And we see glimpses of some city in what looks like Africa being reduced to rubble by an attack. There’s a closeup of Loki’s staff, and everybody looking freaked out on the Quinjet — most of all Bruce Banner, who is holding himself and shaking with a terrified look on his face. People are running everywhere, and the debris is flying like crazy.
Ultron gives a menacing look, as he surveys all the destruction.
Then there are some hero moments: Captain America enters a place shooting some guns. Stuff is blowing up. Banner staggers to his knees in a snowy forest, looking sickly. Thor uses his hammer to smash a tank. Black Widow is in a medical bay, reaching for some surgical tools. We glimpse Nick Fury looking the way he did at the end of Winter Soldier. And Scarlet Widow is on a bus, approaching some people at the back of the bus with magic in one hand.
Tony Stark is looking forlorn and guilty. “It’s the end, the end of a path I started us on,” he tells Black Widow, who says everything ends.
Scarlet Witch sinks to her knees shouting. And there are more shots of Scarlet Witch using her powers, just quick glimpses of her projecting magical energy.
At this point, the trailer strts playing the clasic song “I’ve Got No Strings.”
Tony, in Hulkbuster armor, confronts Hulk on a city street, and there are several shots of them brawling and Tony getting the shit beat out of him. Quicksilver runs through a crowded room that seems to be standing still. Captain America is fighting someone in what looks like a knock-down brawl.
And because this is Joss Whedon, there’s a glimpse of girls doing ballet.
Then we’re back to Black Widow shooting shotguns, and more of the Hulk/Hulkbuster brawl. Thor grabs Tony Stark’s throat and lifts him off the ground. Captain America is riding a motorcycle and then running. Cars are tumbling in mid air. Black Widow touches her hand to the Hulk’s massive green hand, like she’s calming him down. We glimpse a confrontation between Black Widow and Scarlet Witch.
And then Ultron finishes the song saying, “There are no strings on me,” clenching a fist as he celebrates that he’s no longer a puppet.
And we go a shot of Captain America’s shield — shattered to fragments. We pull back, and all of the Avengers are lying prone, apparently dead, in the rubble. Tony is leaning over them, and he looks totally horrified and ashamed.