X-Men: Days of Future Past is out on Friday and represents a unique moment in comic-book movie history. In knitting together the series' original cast, its quasi-reboot cast from First Class and some story threads from the standalone Wolverine movies, Days of Future Past is trying to streamline all these gummy threads into something that makes sense and can have one functional cast moving forwards.

This is tricky business for a 14-year-old franchise, but something comic books do all the time: "retconning" plots and clearing away things fans didn't like through plot devices like time travel. So what's happening in the various X-Men universes that Days of Future Past, directed by Bryan Singer (who made the first two X-Men films), will try to clean up?

In X-Men: The Last Stand (2006), the last film to feature all of the original cast, director Brett Ratner set about ruining everyone's fun by killing off Cyclops (James Marsden) and Professor X (Patrick Stewart), bringing back Jean Grey (Famke Janssen) only to nastily botch her famous "Dark Phoenix" subplot in which she is corrupted with cosmic powers, and de-powering Magneto (Ian McKellen) and Mystique (Rebecca Romijn). It left enough loose threads to suggest that Professor X could be revived and Magneto re-powered, but was so reviled by critics and fans that the franchise then turned to spinoffs and flashbacks rather than attempt to directly follow up this dreck.

In X-Men: First Class (2011), we got a look at the young Charles Xavier (James McAvoy) founding his school for mutants in the 1960s alongside Magneto (Michael Fassbender) and Mystique (Jennifer Lawrence), who turn to a darker path. Aside from them, it largely stayed away from the original cast, giving just a jokey cameo to Wolverine (Hugh Jackman), no mention of Jean or Storm, and a cute nod to Cyclops in the form of a teenager wearing sunglasses. There was also Nicholas Hoult as a young Beast, who Kelsey Grammer had rather adorably played in The Last Stand.

The first Wolverine movie, X-Men Origins: Wolverine (2009), jumped all over time, starting in 1845 and including both World Wars, a sojurn in Vietnam, and then an extended plot in the 1980s that included cameos from a young Cyclops and a returning villain in William Stryker, played as an older man by Brian Cox in X2 but by Danny Huston here. This is where things really stop making sense. Last year's follow-up The Wolverine made the correct choice to stay out of everyone's way by just focusing on a solo plot in Japan for its hero. But it ended with Wolvie being approached by Professor X and Magneto, warning of a dire future and setting up Days of Future Past.

One example of just how messy this business is: '70s Wolverine will sport bone claws, since he hasn't been experimented on yet; but future Wolverine has metal claws, even though those were cut off at the end of The Wolverine and supplanted by the original bone. Bryan Singer says they're back because of Magneto maybe? Really, they're back because Wolverine should have unbreakable metal claws, and that's that. Days of Future Past is taking what it wants from the previous films and ignoring what it doesn't like, and that is the key to any good retcon. 

Where most studios are trying to expand their superhero universes, Fox is looking to streamline the X-Men, not only because some of these sequels were so badly received, but also because a lot of its cast (Stewart, McKellen, Halle Berry) are getting long in the tooth and/or too expensive for such work. They'll still use Jackman (whose character conveniently never ages) as long as they can, but he's been making noise about retirement himself.

I'll leave you with a brief rundown of where everyone is at in the X-Men Universe to prepare you for Friday's release.

Wolverine: He killed Jean Grey at the end of The Last Stand then wandered around in Japan being sad about it in The Wolverine, before fighting a big guy in a robot-samurai suit. In X-Men Origins: Wolverine we saw how he got his metal skeleton from evil mutant-experimenter William Stryker.

Professor X (Patrick Stewart): Blasted into smithereens by Jean Grey, he somehow zapped his brain into another body and approached Wolverine at the end of The Wolverine. This revival was never fully explained; do not expect it to be.

Vintage Professor X (James McAvoy): Paralyzed at the end of First Class by a stray bullet deflected by Magneto. Wheelchair-bound, but decided to found a school for mutants. A little bummed out by the whole "no legs" thing.

Magneto (Ian McKellen): Is he good? Is he bad? He leads a mutant assault against a "cure" in Last Stand, then gets depowered himself. He gets those powers back somehow, and looks to be buddies with Professor X again by The Wolverine.

Vintage Magneto (Michael Fassbender): Disgusted with humanity, he breaks away from his old friend Charles and was last seen freeing Emma Frost (January Jones) from confinement for some evil ends. Emma Frost isn't appearing in Days of Future Past, though, and we all know why. (It's because January Jones gave a monumentally bad performance)

Vintage Mystique (Jennifer Lawrence): After years of suppressing her identity, she embraces her shape-shifting blue form at the end of First Class and breaks away from Charles with Magneto. Older Mystique got depowered in The Last Stand and won't be around in the latest entry.

Storm (Halle Berry): Storm's hanging out. This will be Halle Berry's fourth crack at the role, but she really hasn't done anything of significance in the series, which is a bummer because comic book Storm is the best. (The gulf between the greatness of comic-book Storm and the lameness of movie Storm might be best expressed in this here fan video from YouTuber PlutoPlanetPower, combing Storm voiceover from the animated series with visuals from the movies.)

Beast (Nicholas Hoult): He was just a nerdy kid with big feet in First Class, but an attempt to cure his powers ended up just boosting them further, covering him in blue fur. He was still allied with Charles at the end of that film.

Kitty Pryde (Ellen Page): Remember her? She can walk through walls and stuff! She caused some trouble in the Rogue/Iceman relationship in The Last Stand. In the comic books, Kitty (aka Shadowcat) is the protagonist of the "Days of Future Past" storyline, but that business is being handed to Wolverine for the movie.

20th Century Fox

Iceman (Shawn Ashmore): Iceman was seen holding hands with Rogue at the end of The Last Stand, where he also finally figured out how to transform his whole body into ice, which is his standard form in the comic books.

Rogue (Anna Paquin): Rogue's apparently gonna be in this one for a hot second after most of her scenes got left on the cutting room floor. She got voluntarily de-powered in The Last Stand.