The movie is about Sarah Paulson's character, Dr. Staples, was able to capture both David Dunn and The Horde (McAvoy's character) and put them in the same insane asylum as Mr. Glass as you know from the trailers. Her agenda was to have them disbelieve that they are super-powered beings like in the comics. Her plan was to low-key lobotomize them with Mr. Glass being the first, but Mr. Glass while playing possum pretending he's already brain-dead already devised a plan to escape. He linked up with the Horde and convinced him that he was indeed a super-powered being and they're meet the next day to escape. Then he swapped glassed object from the operating machine so the lobotomy procedure would fail unbeknownst to Dr. Staples. That night Mr. Glass kills one of the medical security aides, freed The Horde, but prior to that, Mr. Glass hacked into the computer system and reworked all the video security cameras. He then went on the speaker mic to let David Dunn know that him and The Horde had escape and heading to the new tallest building in Philly to cause havoc and that Dunn have to use his superhuman strength to breakout the maximum secured steeled locked door in order to stop them and save the city. Then said his intention was for the entire world to know that superheroes to exist. Knowing from what Glass did in Unbreakable in doing such mass murder, Dunn was able to break himself free. Mr. Glass and The Horde went downward to the basement area where they are all visible and The Horde proceeded in killing off some of the guards while going through there. Meanwhile, Dunn's son, Mr. Glass's mother, Mrs. Price, and Casey from Split (who now has an affinity with The Horde because she's the only one who understands him) all met up at the asylum to try to prove to Dr. Staples that none of them are crazy and that superheroes are indeed for real. Dr. Staples have them some BS excuses, but then learn about them escaping the asylum. She alerted the police with strict instructions of none of them to make it out the premises. Dunn catches up with Mr. Glass and The Horde out on the parking lot area. As Dunn and The Horde start fighting, Mr. Glass was commentating speaking how it's like in the comics. Dunn's son, Casey and Mrs. Price comes out and spectated what's going on. The police comes in with body armor and shields and attempted to break it off between Dunn and The Horde. Dunn was able to push all of the police on him back into a container and locked them in while The Horde savagely was beaten the police that's on him to a pulp. Once they both taken care of the police, they were about to return back fighting. Mr. Glass tells The Horde that Dunn is water and he needs to toss Dunn into the water tank, but before The Horde was about to do that, Dunn's son intervened and said that Mr. Glass organized the train wreck that killed The Horde's father which inadvertently birthed The Horde's multiple personalities. The same train wreck that David Dunn was on. Mr. Glass was both shocked and pleased with this reveal as he saw it as not a coincidence but fate that he's responsible in the creation of these super powered beings. The Horde wasn't at all pleased because The Horde's whole purpose, especially the persona of THE BEAST, is to protect Kevin, the original host. And learning that it was Mr. Glass all along that was the cause of all of it, The Horde crushed Mr. Glass's shoulder (as a reminder, Glass' entire skeleton is brittle). Dunn intervened telling the Horde to stop which pleases Mr. Glass again in that it's the hero coming in to depend the villain cliché. The Horde proceeds to attack Dunn again, but not before he pushes real hard into Glass' chest and his entire chest caves in and he falls crushing more of his bones and begins to die from internal bleeding and a caved-in chest. The Horde tosses Dunn into the water tank and starting fighting him inside the tank. Dunn, while struggling was able to pound on the walls of the tank and the tank breaks. As he struggles to regain strength, the police comes through and starts slamming him into a puddle. The Horde was intervened by Casey who has the power of an empath and was able to get the original host, Kevin, back. Once Kevin was back, he was immediately shot by the police and he dies. The police is still slamming Dunn into the puddle. Dr. Staples told Dunn to reach out her hand like she was going to pull him off. He tries and once he touches her hand, he learned what was the first BIG TWIST, which is she was part of a secret society that's been going on for centuries, similar to The Court of Owls in Batman, and their whole purpose is trick the world that GODS don't exist. Therefore, if they ever encounter anyone that have abnormal abilities and believe they are superhuman in any way, they do whatever it takes to kill them off. Dr. Staples, intent was to originally be more humane and have them believe it's all in their heads, but because that failed, she ordered the police (which was actually hired security of the secret society) to kill them off. With this reveal, Dr. Staples proceeded for her police to drown Dunn in the puddle and Dunn dies from drowning. So, Mr. Glass, David Dunn, and The Horde are all dead. Which I presume is why people would be pissed. But that's not the end of the movie. The aftermath focuses on Dr. Staples. She tells all the employees, the security and so forth that everything is under control and back to normal. Justified why they were killed because of the lives of the guards that were killed and told them that none of what happened should be spoken about outside the asylum. Then she conducted a secret society meeting with her people explaining the situation and comforting their concerns of the risk of the reveal of superheroes existing among us. However, once she went back to the office, she realized that the video cameras were tampered, thus the 2nd twist. As I mentioned earlier before that Mr. Glass tampered with the security cameras. The whole reason was so that it can record EVERYTHING that occurred, the fight, the powers, everything. Then he had it downloaded it and sent to Dunn's son, his mother's, and Casey's email address. Dr. Staples, in shocked because Mr. Glass had all of this planned the whole time and knew he was going to die regardless. His whole intention was for the entire world to learn about the existence of superheroes and he knew all along about Dr. Staples. Dr. Staples, devastated because she knew that she's doomed from this about to be exposed. The movie ends with Dunn's son, Glass' mother, and Casey meeting at the same train station as where all of it originated and wait for the reaction of people as they sent it viral online. And it ends with them proud that people will soon learn that superheroes do exist and more should come forward instead of hiding.