(M) ****

Director: Bryan Singer.

Cast: Hugh Jackman, James McAvoy, Michael Fassbender, Jennifer Lawrence, Peter Dinklage, Patrick Stewart, Ian McKellan, Nicholas Hoult, Ellen Page.

TIME travel is a notoriously tricky device to use in movies. 

Adding more characters with every increasing sequel (especially in comic book movies) is also fraught with danger.

With this in mind, the seventh movie to be based on the comic book mutants known as the X-Men isn't just playing with fire, it's juggling lit dynamite. 

Returning director Bryan Singer has taken the cast of the original X-Men trilogy and combined them with the stars of the prequel X-Men: First Class in a decade-jumping story set both in 1973 and 2023.

In spite of the difficulties, or perhaps because of the way the film embraces these elements, Days Of Future Past is one of those increasingly rare things - a genuinely excellent X-Men film (alongside the 2000 original, 2003's X2 and 2011's First Class in case you're wondering how long that list is).

In 2023, the few surviving mutants fight running battles against the Sentinels, a bunch of murderous robots that ran rampant and ushered in a dystopia for mutant-kind and human-kind.

Among the last of the X-Men are Professor X (Stewart), Magneto (McKellan), Kitty Pryde (Page) and Wolverine (Jackman), who figure the best way to end the war with the Sentinels is to use Kitty's powers to send Wolverine back in time and stop the madness before it begins.

That will involve Wolverine visiting 1973 and convincing younger versions of Professor X (McAvoy) and Magneto (Fassbender) to work together to prevent shape-shifting mutant Mystique (Lawrence) from kick-starting anti-mutant sentiment when she shoots Sentinels inventor Bolivar Trask (Dinklage).

It sounds complex and weird when you lay it out like that, but Days Of Future Past feels surprisingly linear and straightforward when its happening. Deftly edited so as to keep events focused, the film rockets along at a solid pace, and while comic book movie fans of the future will surely poke holes in its time travel structure, for the present it seems to work.

As for that other potential problem of having two many comic book characters - otherwise known as Batman & Robin Disorder or Spider-Man 3 Syndrome (depending on whether you prefer DC or Marvel) - Days Of Future Past deals with it in the best possible: by simply ignoring the problem.

Rather than worrying about ensuring every character has an arc, it uses its multitude of mutants as either plot devices, weapons or key players.

For example, Quicksilver (Evan Peters), Kitty Pryde and even Wolverine don't get much in the way of development but their powers mean the plot couldn't happen without them (and Quicksilver's main sequence is as awesome as Nightcrawler's White House break-in in X2).

As for the majority of cool-looking mutants with neat names - Toad, Spike, Ink, Havok, Blink, Sunspot, Warpath, Colossus, Bishop - they're here to fight, preferably while demonstrating their special abilities. Most of them are only here as fan-bait and thankfully the film doesn't bother overloading its story with lesser unnecessary character subplots.

The key players, as with First Class, are Professor X, Magneto and Mystique, and Simon Kinberg's screenplay doesn't short-change their fascinating relationship triangle. It's a shame Wolverine and Beast (Hoult) don't get much more to do than quip, fight and give pointed looks, but it's a relief in a way because it means Days Of Future Past can strike a balance between its stunning action sequences, its central three-way character interaction, the continuing discrimination themes of the series, and its fan-baiting and in-jokes.

The end product is suitably lean, while managing to be a perfect blend of all-audience sci-fi actioner and fans-only nerd-out (there are some great cameos at the end for the true X-fans).

But when you consider much of the cast has either won or been nominated for an Oscar and that Singer was responsible for two of the best X-movies (X-Men and X2) perhaps it shouldn't be so surprising that Days Of Future Past works so well.