In Eastern Europe—specifically the imaginary country of Sokovia--the Avengers are raiding a Hydra location where Baron Wolfgang von Strucker (Thomas Kretchmann) is experimenting on humans with Loki’s scepter. We meet Quicksilver (Pietro Maximoff, played by Aaron Taylor-Johnson) who moves with superhuman speed, and the Scarlet Witch (his sister Wanda, played by Elizabeth Olsen) who has telepathic and telekinetic powers. The Avengers apprehend Strucker, and Tony Stark (Robert Downey Jr.) gets his mitts on Loki’s scepter. The long first-scene battle, which plays like the pre-title action of a Bond-movie, involves the entire Avengers line-up against Strucker’s army, and pauses for one of those wide-screen stills reminiscent of a double-page spread in a comic book.

Stark and Bruce Banner (Mark Rufallo) find that the gem in the scepter is artificially intelligent, and they use it to complete Stark’s Ultron Global Defense System. What could go wrong? Ultron (James Spader) turns out more sentient than they expected and decides the best way to save Earth is to eliminate the most dangerous species on the planet—the humans. Where have we seen this before? He destroys JARVIS—Stark’s AI—and attacks the Avengers at their HQ. He gets away with the scepter and uses it to perfect his robot body and build a robot army. What else? He kills Strucker and recruits Quicksilver and the Scarlet Witch, who blame Stark for the deaths of their parents in a bomb-blast. Then he raids the HQ of an arms-dealer named Ulysses Klaue (Andy Serkis in a rare recognizable role) in Johannesburg, to obtain vibranium from the Kingdom of Wakanda. The Avengers attack Ultron and the Maximoffs there, but Wanda gives them visions and Banner Hulks out, so Tony must subdue him with his new armor, which was designed specifically to stop the Hulk. Always thinking ahead of the curve, that guy.

The World, for some reason, reacts badly to Iron Man/Hulk destruction in the streets and, still tortured by Wanda’s visions, the Avengers go into hiding at Hawkeye’s (Jeremy Renner) secret farm. Thor’s (Chris Hemsworth) visions had been about the apocalypse and he leaves to find Doctor Selvig (Stellan Skarsgaard) to help him understand. Nick Fury of SHIELD (Samuel L. Jackson) arrives to help the Avengers plan an assault on Ultron, who is in Seoul, using the scepter to enslave Doctor Helen Cho (Claudia Kim) to use her synthetic tissue, the scepter’s gem, and the vibranium to build himself an indestructible body. But as his intellect becomes more human, Wanda reads his mind, discovers he is out to eliminate the human species, and she and her brother turn against him. Captain America (Chris Evans), Hawkeye, Black Widow (Scarlet Johansson), and the Maximoffs—all of whom constitute the second iteration of the Avengers in the comics, manage to retrieve Ultron’s new synthetic body, but Ultron captures Black Widow.

JARVIS still exists, hiding in the internet, and Stark and Banner secretly load him into the synthetic body. Many of the Avengers, rather peeved at the way those two geniuses have been so stupid, argue like a typical Marvel family. Thor returns to activate the body because the gem on its brow is the Mind Stone, another one of the six powerful Infinity Stones that are popping up everywhere in these movies. The resulting being awakes, who is Vision (Paul Bettany, who has been the voice of JARVIS all along), and the Maximoffs go to Sokovia with the Avengers, where Ultron is busy lifting the capital city into the sky to crash it to earth, triggering apocalyptic earthquakes. Are you following this?

Banner rescues Black Widow, who triggers the Hulk, while the Avengers battle Ultron’s army, all of which are him. Nick Fury arrives like the Cavalry in a Helicarrier with agent Maria Hill (Cobie Smulders), James Rhodes as War Machine (Don Cheadle), and SHIELD to evacuate civilians. The big finish reminds me of the Cities in Flight novels by James Blish. Nothing tops a climactic Helicarrier battle like entire cities falling from the skies. It’s pretty spectacular. At the end, the Hulk sets out for parts unknown—he’s taken a shine to Black Widow and is afraid of hurting her. Vision destroys Ultron’s last remaining body—we think. The Avengers have a new base run by Fury and SHIELD. Thor returns to Asgard. Stark leaves on some no doubt secret and dicey mission of his own. Hawkeye returns to his family. Captain America and Black Widow train the new Avengers recruits. And the Titan Thanos decides to gather the Infinity Stones himself.

All this, described this way, sounds a little, shall we say, hard to believe—like a comic book—but there is much to keep your senses busy: Joss Whedon’s sharp humour, amazing spectacle, action, emotion, intramural conflict, revelations concerning characters’ back-stories, and James Spader’s hypnotic voice and thoughtful, if appalling, philosophical musings. Considering how many characters are involved and how complex the plot, it’s surprising how easy it is to follow the story—at least in a second viewing, on the small screen. One of the most impressive special effects in the movie was hiding Scarlett Johansson’s pregnancy.