Beginning in a post apocalyptic world where giant robots hunt down mutants, a handful of our old friends from X-Men 1-3 fight for survival. Old feuds have been set aside as Magneto, Xavier, Storm, Wolverine, Collossus, Kitty, Iceman, (Ian McKellen, Patrick Stewart, Halle Berry, Hugh Jackman, Daniel Cudmore, Ellen Page and Shawn Ashmore) and a couple of newcomers  battle the brutal killing machines. Using Kitty’s time travel powers, they hatch a plan to send Wolverine back through time to prevent the creation of the robots in the 1970s.

Playing with time travel is dangerous. It raises scary ethical questions like whether Wolverine should take the opportunity to kill Juggernaut at birth. But it’s also dangerous for a film’s plot, particularly one with an established timeline.  If you’re going to shake up the universe people have invested in for 6 films you have to make sure it’s good. Luckily Days of Future Past is the best X Men film to date, managing to be sincere and thought-provoking through its elaborate, cross-time expanse.

I said in my recent review of X Men: The Last Stand that it felt like they were doing the bare minimum to get to the end battle. Days of Future Past is the polar opposite of this, with the multi-faceted plot coming well before considerations of where the action is going to happen. That’s not to say there isn’t some superb action, which makes the best use of the X-Men superpowers of any of the films, and flawless special effects to match, but that this is secondary to the story.

Wolverine is sent back to convince young Magneto and Xavier, who are not on speaking terms, to unite to stop Mystique (Jennifer Lawrence) from inadvertently allowing her DNA to be used to create the robots. As a consistently interesting secondary character, it’s nice Mystique is now the focus of the plot, building on what we learnt about her in X2 and First Class. Wolverine’s position as the outsider in the group, and also the only mutant able to carry his own film, is acknowledged by making him the go-between, connecting past and present.

To write a film featuring all the surviving characters from the ensemble X-Men films was an almighty challenge. It risked falling into the trap of having characters tokenistically show up to give a wink to the audience and leave, like The Expendables 2. But all mutants, past and future, feel relevant to the film, and there are even a few faces here no-one expected to see. It benefits from outstanding performances, particularly from Fassbender, McAvoy and Jackman. Fassbender’s accent woes have cleared up, and we get more of a sense of the Magneto/Xavier friendship than in any other film.

It also gets the tone just right, even better than series high points X2 and First Class. It knows when to be serious and when to be light, and the characters feel better rounded and more thoroughly developed than ever before, even in spite of how crowded the screen is.

Days of Future Past isn’t just a fitting way of uniting the new and old X Men, it sets the bar very high for ensemble superhero movies, with a maturity we have yet to see from the Avengers franchise. If this was to be our farewell to the world of mutants it would be a fitting send-off, but I suspect there’s plenty of life in the old guys yet.