Ok here is what happens in this movie.
Spoilers.
Spoiler:
It opens with Reed and Ben as kids trying to build a teleporter. Over the years, they get a prototype ready and Reed shows it off at the school's science fair, and attracts the attention of the Baxter Institute, a research center funded by the government. So he's brought into the group by Dr. Storm and meets Sue, Johnny and Victor. Ben doesn't feel at home at Baxter among the scientists and he and Reed drift apart.After some years, Baxter finally has a fully functioning big teleporter working. Reed and Sue grow close, which gets Victor jealous. He was once Storm's protege, the future of Baxter and had feelings for Sue, but now Reed has taken all of that. The group displays the machine to Tim Blake Nelson's character and he authorizes an expedition.
Reed, Sue, Johnny and Victor are set to go, and Ben is brought along because Reed promised him he'd be there. They go into the other dimension and learn it's a dying planet filled with glowing lava-like substance. Victor is reckless, trying to get a sample, which leads to the mountain they're in collapsing and they all getting exposed to the planet's strange energies. Victor falls into the lava-looking shit and is presumed dead, while the others make it back to Baxter.
Anyway, the other four now have superpowers. Nelson takes over, takes them to a facility built to house them and their powers, and announces he wants to weaponize their powers. Reed is blaming himself for what happened, particularly to Ben, and wants to find a cure. Since they're now property of the Army and Storm can't help them, Reed bargains to help the military in a series of operations to show off to Nelson's superior their combat effectiveness, and let Nelson's top men study them so they can reproduce their powers, in exchange for Nelson giving them the money and the tools to find a cure. Storm isn't very pleased with that.
Meanwhile, we see Victor survived, has powers too and is left to roam the dying planet.
We get a montage of the Four in missions across the globe, and they're good, but they don't follow orders to the letter. They let some unarmed soldiers go, they hesitate, they're cocky, that kind of stuff. Some time passes (it's not quite clear how much), and Storm finds out Nelson has secretly stolen Reed's designs from Baxter and is building another teleporter. He wants to send soldiers to the dying planet to get samples of the lave-like radioactive goo so they can have a supply to keep pumping out supersoldiers. The FF object to this, but can't do anything about it.
So Elder opens the portal, and once the soldiers step into the dying planet, they're pretty easily killed by Victor (now "Doom"😉, who steps out of the portal and fights them. He has telekinesis, can control other peoples mind, energy blasts, molecular manipulation, all kinds of shit. Sue eventually knocks him out with her force fields and he's detained.
Nelson thinks Doom is the game-changer. Reed talks with Victor and tries to offer help, but Victor refuses. He sees himself as a god and wants to conquer Earth. Nelson says that, since Victor is technically "dead", they can do whatever they want, and decides to vivisect him to explot his powers. Reed objects and says he can find a cure.
Nelson decides to be an *******, detains the FF in specials cells he created for them without them knowing, and destroys all of Reed's research on cure and laughs about it to their faces.
Victor is prepared for vivisection just as some technicians find out the computers are acting strange. Victor has technopathy too, and he is basically downloading all the data directly into his mind. He then breaks out and begins killing everyone. Storm is at the base and helps the FF escape. He wants them to flee from the government, but they decide to stay and fight. Doom ends up brainwashing the Johnny into attacking Sue and soldiers into attacking Reed and Ben.
He destroys the new teleporter and then Storm shows up with a gun and tries to kill him. Doom stabs Storm, saying Storm was the only one that ever treated him as an equal, and he's returning that favor by sparing Storm of seeing his children die. Storm dies, Sue goes apeshit and creates a force field so strong it knocks down power on half the city. Victor is injured and escapes.
The teleporter's destruction has created a series of ripples in the space-time continuum, that'll eventually become a singularity and destroy all life on Earth. The FF then convince the military higher-ups to give them 24h to solve the crisis before they attempt to evacuate the population from the endagered areas, since nukes don't matter.
They outfit an old plane with Reed's teleporter and use it to launch themselves into the dying world, where Victor is guarding a massive tower of energy, increasing the singularity's mass so the end of the world arrives faster.
The FF fight Doom and get rekt at first, because Doom is so much more powerful, but Reed then gives them a pep talk and they all combine their powers and fight as a team. Together, they defeat Doom and destroy the tower, causing the dying planet to begin to collapse. They jump into the thresold of the portal Victor had opened, while Victor is left behind, seemingly to die, and manage to journey back to the Earth.
The singularity is still near critical mass, but Sue manages to contain it with a massive force field, and the Earth is saved. The military recognize the FF for their superhero efforts and fire Nelson. Reed takes over Baxter and decides to focus on starting to search for a cure again, but the others tell him it's not necessary. Their powers are a gift and can be used to change the future as Storm always wanted. Reed makes them new uniforms (which look pretty good) and decides to look over his old models for a flying car, which I guess is teasing the Fantasticar. Reed and Sue get together. Happy end.
Cut to a snow-covered village in some nameless Eastern European country. Soldiers are rounding up the locals, being dicks, even beating some people. They see a man cowering in a corner, with a cloak over his face, and start dicking around with him. You can guess where that's going, right? It's Doom, and he prepares to kill the soldiers as the movie cuts to black.