Thanos, the titan, has a plan. He is rebalancing the universe by killing off half the population, planet by planet. That's a slow and tedious process, but if he was able to gain control over the six Infinity Stones, he would be able to reach his goal simply by clicking his fingers. After a deadly encounter with what remains of the Asgardian population, he turns his eyes towards Earth, where two of the stones are located, one of them in Vision's head. The Avengers reform to take on the threat of Thanos' children and prevent him from getting those two stones. In space, that task falls to the Guardians of the Galaxy and a grieving Thor. Defeat after defeat leads to final climactic battle in Wakanda where Earth's mightiest heroes take on the alien threat with the fate of half the universe hanging in the balance.

All of the Marvel Cinematic Universe films have been leading up to this, the first of a two-part conclusion the saga that has been running since the Tesseract first appeared in CAPTAIN AMERICA:THE FIRST AVENGER. This has been the most ambitious piece of narrative cinema ever attempted, a single tale told over a number of films starring various characters, each film having to satisfy in its own right as well as moving the main plotline forward. After a set up like that, this conclusion (along with AVENGERS:ENDGAME) needed to be something very special indeed. Fortunately, it manages to pull of the seemingly impossible task of bringing all the plotlines together in a satifying, somewhat shocking, penultimate episode.

With the finale to come (and at least one film set before the events of this one), AVENGERS:INFINITY WAR was never going to be a complete film, necessarily acting as an extended set up for the big finish, but the point to which the story is taken is a fascinating one, though also one that cannot be discussed in any details without spoilers that really should not be given. Suffice to say that it is very hard to see how the writers are going to bring us back from this one.

The film has a very long running time (two and a half hours), but that's because there is so much plot to actually fit in, so many characters to find something to do and so many action sequences to crash against the audience's eyeballs. With all that is going on in the film, it never feels long or drags. The characters that are featured (the main Avengers and the Guardians of the Galaxy) have plenty to be getting on with as there are attacks on Edinburgh, New York, Titan and Wakanda with lots of CGI destruction, something the film-makers can handle with great ease at this point. The villains are as strong as the heroes (or stronger in the case of Thanos), but also disappointingly mainly CGI. The children of Thanos are given very little personality and are really only there to allow for extensive destruction to be wrought before the big purple people eater (OK, Thanos doesn't eat people, but he kills them, half of them at least) himself shows up to get to the really dirty work. The ball is set rolling with a post-battle scene on the Asgardian refugee fleet, which sets the tone as some of the most powerful, and favourite, characters are comprehensively handed their arses. This villain is serious and make no mistake.

Any superhero film is only as good as its villain and, in Thanos, AVENGERS:INFINITY WARS has one of the strongest and most nuanced nemeses yet. Not just a killer out to amass ultimate power, his delusion that his universal genocide is for the good of those remaining, gives him some depth and real character. His encounter on Vormir with his daughter Gamora (no spoilers) adds to the three-dimensional nature of the character, making great use of Josh Brolin's voice and manipulated image. His alleged altruism is undermined by the manner in which he enjoys the pain he inflicts, but that just makes for a more complicated enemy than most.

For the heroes, there is much less character work to be done, since that's already been achieved in the films leading up to this. The actors all know their characters inside and out and mainly just get to athletically bound around and hurl big objects, mystical or technological energy bolts and one-liners with equal abandon. Robert Downey Jr remains the central figure as Tony Stark/Iron Man, but Benedict Cumberbatch steps up as Steven Strange, master of the mystical arts to act as a de facto second in command. Tom Holland's Peter Parker is the comedy sidekick to their duelling egos. Meanwhile, the collision of the Guardians of the Galaxy with the God of Thunder is full of wit and verve, as you would expect. The trip to a galactic scale dwarfs' smithy (Oh, that just has to be a big shout out to Tolkien) makes very little sense, but with a talking Racoon and Peter Dinklage as a giant dwarf(!) it would be almost churlish to complain. The heart is provided by Paul Bettany and Elisabeth Olson as Vision and Wanda Maximoff, whose love has come out of nowhere to add some personal stakes to the proceedings.

Everyone else is pretty much just along for the ride, some showing up in Wakanda for the big battle climax only. This action sequence is huge, as is only to be expected in the final third of a superhero film these days, but the audience has been along for the ride for a while now (anyone coming into this as their first MCU film won't have a clue what's going on and serve them right) and the big payoff in terms of spectacle and destruction is everything they could ask for.

Everything here has been honed to be as slick and spectacular a piece of entertainment as possible. There is barely a wasted moment and nobody stumbling out of the cinema after that ending will have any cause for complaint. Bring on the Endgame.