Professor X and Magneto have teamed up at some unspecified point in the X-Men’s future, they face giant power-morphing robots that are designed to hunt mutants but are on the verge of destroying the world. The only way to stop it is to change the past.
This gives us a reason for Wolverine to travel to the past using Kitty’s new consciousness time shifting powers (she’s the one that walks through walls in the trilogy) (also, don’t think about it too hard because it doesn’t make much sense).
Wolverine goes back to meet the younger Charles Xavier in the past to persuade him to ally with Magneto in stopping a public murder of an important man. That murder shows mutants as dangerous and causes the end of the world timeline that they need to avoid.
This all results in a high stakes survival movie where only some of the characters really understand what’s going on. We get to see the desperation of the trilogy X-Men and their new allies as they battle something they cannot possibly stand against, while also watching a story about how countering racism with violence is wrong; this story is also a chase to stop their history’s greatest infiltrator from doing what she intends, a choice of greater good versus personal gain and a way to see the destructive methods of Magneto.
This movie takes the best bits of both the old and young X-Men and rams them together in a way that if we do treat this as a stand-alone film then it may be the best the X-Men has to offer. It’s big, flashy, has some great actors as well as great scenes and a plot that has peril for everyone involved. It’s not one of my favourites because of how the timelines are so messed up that it becomes confusing, but if this had been the only X-Men then it’d be a pretty great movie.
SPOILER (sort of): This movie’s conclusion does change a lot about the X-Men series, Stryker takes Wolverine in the seventies which means parts of X-Men Origins could happen but Jean Grey is alive in present day so the X-Men trilogy didn’t happen. This film wipes out quite a bit of the main timeline which provides them with the opportunity for a fresh start to use the characters differently for roughly thirty years worth of their history. Or DoFP could just be seen as a stand-alone, spin-off ‘what if?’ situation.