In 1961 in Philadelphia, a woman gives birth in a department store. Soon the doctor arrives and checks on the baby, who won’t stop crying. To his shock, the baby has fractured his legs and arms in the womb.
Many years later, David takes the train back to Philadelphia after a job interview in New York. When he sees a woman is about to sit next to him, he takes off his ring and hides it in his pocket. They chat about sports and he mentions he’s afraid of water, also that he doesn’t like football.
He also tries flirting with her, but she turns him down and moves to another seat. Then David puts on the ring again. Suddenly the train starts going faster and everything shakes around David.
At home, David’s son Joseph is watching TV and the news show a train that just derailed, killing everyone inside. Panicking, David checks the notes to realize his dad was on that train. Moments later at the hospital, David wakes up and notices a person being operated on nearby before he’s found by a doctor, who asks for his history.
David explains he’s never had any allergies or underlying conditions and is surprised to learn he’s the only survivor from the accident. In fact, the doctor is amazed by David's lack of pain and injuries, not even a single scratch. When David leaves the room, he finds his family waiting for him.
Joseph tries to make David and his mom Audrey hold hands, but they quickly drop it. Later at home, David tells Audrey that he doesn’t think he got the job, but he’ll move out soon anyway. It turns out they’re separated and sleeping in different rooms.
The next day, David attends the memorial service for the 177 deaths of the accident. After it’s done, David returns to his car and finds an envelope with a card that has the “Limited Edition” logo. When he opens it he finds no names, just a note asking him how many days he’s been sick in his life.
Afterward David goes to work, which consists of being security for a football team. With the card still on his mind, he asks the secretary to check how many sick days he’s had. Then he watches the team train with nostalgia in his eyes.
At the end of the day, David is told by his boss that he’s never had a single sick day since took this job five years ago, so he’s getting a raise. That night David asks Audrey if she remembers him ever getting sick, because he doesn’t. Audrey thinks about and admits she can’t think of a single day of seeing David sick since she met him in college.
A flashback jumps to 1974, where the baby from before is now a teen. It turns out he has osteogenesis, which means all his bones are very fragile and he often ends up breaking them. The boy is afraid of going outside and getting hurt again, not to mention other kids at school call him “Mister Glass”.
To take him out of his isolation, his mother tells him she left a present for him outside. The boy gathers his strength and gets the gift, which happens to be a comic book. His mother explains he’ll get another one each day he leaves the house.
In the present, the boy has grown into an adult. His name is Elijah and he has an art gallery dedicated to comic book art. He’s very defensive of comics as an art form and cancels a sale when he hears the client wants to give a valuable painting to his four-year-old.
In the afternoon, David and Joseph come to see Elijah to ask about the card. Elijah explains he’s interested in David’s health and is glad to hear he was never sick, however Elijah did have an injury: in college, he was in a car accident that hurt his leg and made him quit football. Then Elijah explains he studied comic books all his life and he thinks superheroes are based on old history.
Because of his health condition, he’s always wondered if there was someone else out there that was the total opposite, meaning someone unbreakable. When he heard Elijah was the sole survivor of the train accident, he thought he could be the one. Joseph is excited about the possibility of his dad being a superhero, but David thinks this is some weird scam and leaves with his son.
That night, David reads about the accident on the newspaper, which inspires him to check his closet. He has a gun hidden there and a folder with newspaper clips related to his life. The first ones show his the start of his football career and the last one is the car accident.
The vehicle is really damaged, so the fact he survived it’s a miracle. At that moment he’s interrupted by Audrey, who asks him if he’s been with any other person. After David says he hasn’t, Audrey admits she’s been shaken by the train accident and announces she would like to work on their relationship again because his survival is a sign of second chances.
Sometime later, Elijah visits David while he’s at work, telling him it was no coincidence that he chose security as his job because his instincts want him to protect people. While they walk near the line, David stops to look at a particular guy and thinks he’ll leave before he can be patted down. Just as he predicted, the man soon walks away.
Elijah wonders how David knew that guy was carrying a weapon, so David explains he sort of got an image in his head showing him. In fact he has a natural instinct to tell when someone has done something wrong. Elijah calls it his superpower, but David doesn’t like where the conversation is going and asks him to leave.
Before doing so, Elijah asks if someone else had been in the car accident, and David confirms Audrey had been there too. Afterward Elijah goes to his car and sees the supposedly-armed man passing by. He starts to follow him and even asks him to wait, but the man ignores him.
Elijah tries to go as fast as he can considering his condition, but he’s still too slow. When the man goes down the subway station, Elijah pushes his body too far and falls, breaking multiple bones. As his cane breaks and he deals with the unbearable pain, he sees the man’s shirt move and reveal the gun hiding underneath like David predicted.
After the match is over, David goes home and sees Joseph playing football. He scolds him for it, reminding him that Audrey hates the sport because of the injuries that causes. Then David decides to do a little experiment and starts lifting weights.
At first it’s just 250, the most he’s ever lifted. Joseph keeps adding more and more with each try until they’re using every weight they own. Wanting to learn more, they also add some cans of paint and David ends up lifting 350 while barely breaking a sweat.
At the hospital, Elijah is told he has multiple fractures, but the worst are the fourteen ones in his leg, for which he’ll need physical therapy. Later he ends up attending physiotherapy with Audrey and uses the chance to ask about her marriage while pretending to simply wanting to know his doctor better. He learns that that David's car accident making him quit football is what got them together since she can’t stand the sport and the harm it causes.
While asking more questions, Elijah accidentally says David’s name and Audrey gets suspicious. Elijah shares his theory but Audrey doesn’t know what to think. During another match, David decides to stand in the middle of a crowd and any time someone bumps into him, he gets a vision.
At first it’s just the voices of a yelling kid, but then he sees a man suspiciously picking something from the trash. Suspicious, David makes the guy step out of the line to search him, yet he finds nothing in his pockets. David decides he was fool to believe he had a power.
At that moment David gets called to the school because Joseph was hurt. The teacher explains Joseph got in a fight and wonders if David remembers her from when he studied there. She tells the story abut the time child David fell in the pool and laid on the bottom for five minutes.
When they pulled him out, he was dead until the paramedics revived him. In the end they changed the rules of conduct around the pool because of him and the kids share the story as an urban legend. Hearing this makes David even more convinced he isn’t a superhero.
After they leave the school, Joseph explains he got in a fight because he protected a girl that was being harassed for her race, saying he wants to be a hero like his dad. David tries to insist he’s normal, but Joseph doesn’t believe him. In the evening, Audrey tells David that Elijah told her everything.
Before they can discuss it, they discover that Joseph has grabbed David’s gun and points it at him, wanting to prove he can’t get hurt. The kid hesitates for several seconds and David manages to talk him into putting it down. The next day, David visits Elijah, who immediately confirms the man from the stadium had a gun.
Elijah also thinks David didn’t get hurt during the car accident, he made up a lie to quit football so Audrey would date him. David doesn’t want Elijah to bother him or his family anymore and tells him how he got pneumonia as a kid because of the time he almost drowned, which should be enough proof to drop the subject. Later Elijah is at the comic book store in a not responsive state.
The clerk needs to close the shop so he starts dragging Elijah out in his wheelchair, but Elijah keeps moving the wheel to make him mess up. After a few tries, Elijah finally talks when he finds the comic he wants. Meanwhile David and Audrey leave Joseph with a babysitter so they can go out on a date.
They have drinks together and try to reconnect, forcing David to admit he’s kept his family at arm’s length because something doesn’t feel right. When they come back, the babysitter tells them she picked a phone call from New York saying David got the job. However the family assures her they aren’t going anywhere.
There’s also a message on the machine from Elijah, explaining every hero has a weakness and David’s kryptonite is water. Desperate for answers, David sneaks in the middle of the night to find the train from the accident. He looks at the destroyed car and knows nobody normal could’ve survived it.
This triggers the memory of the car accident and it’s revealed he got out just fine, but Audrey had been stuck inside the burning vehicle. David used his super-strength to rip the car door off and save Audrey. Soon someone arrived to help and David realized it was weird for him not to be hurt.
Overwhelmed by the memory, David calls Elijah and admits he never suffered an injury in his life, wondering what he should do. Elijah tells him to go where people are. Moments later, David goes to a crowded area and opens his arms as he starts looking into people’s crimes on purpose.
He sees a woman distracting a clerk to steal jewelry, a guy throwing a bottle at a black group while insulting them for their race, and a guy taking advantage of an unconscious drunk girl. When he bumps into the janitor, he discovers the guy killed a man to take over his house. David waits for the janitor to finish his work and follows him to the house, noticing he enters through the back door.
Following the same route, David gets inside too and discovers the place is a mess, not to mention the owner’s body is still on the stairs. Then he looks around the rooms and finds two kids tied up in a closet. David immediately frees them and asks them to be quiet.
Next David checks the main room and finds the mother tied up as well. The balcony door is open and David steps through it, thinking the guy may’ve escaped. At that moment the janitor appears behind David and pushes him off the balcony, causing him to fall on a wet surface.
David looks around and realizes he’s on a pool cover, which slowly begins to sink under his weight. Entangled in the fabric, David can’t swim and keeps struggling to breathe and survive. Thankfully a stick suddenly appears in the water and he grabs it so he can be pulled out.
It turns out the kids have come to rescue him. Afterward David returns to the main room and grabs the janitor from behind to choke him. The man fights back and pushes David against the wall, which causes damage on the surface.
David is still stronger and manages to kill the guy in the end. Then he frees the mother, but unfortunately she’s already dead. That night, David takes Audrey from her room so they can sleep on the same bed again, the feeling of something wrong finally gone.
The next morning, Joseph sees his parents are behaving very lovingly with each other. When Audrey is distracted, David shows Joseph the newspaper with the news about the dead janitor, which includes an illustration of a mysterious vigilante. David confirms it’s him and asks Joseph to keep the secret.
Sometime later, David goes to Elijah’s art show and meets his mother, who tells him about the two types of villains: those who fight with his fists, and those who fight with his minds. The woman has heard about David because Elijah calls him a friend. Then David follows Elijah to his office and Elijah congratulates him on his first night as a vigilante.
He offers to shake hands and when they do, David makes a shocking discovery: for years, Elijah has been causing accidents on purpose to find a superhero, including the train David was in. Shocked, David looks around and notices Elijah’s plans and research. Elijah explains that now David knows who he is, he also finally knows his own identity: the villain to David’s hero.
Like in the stories, they’re the exact opposites yet sometimes also friends. Perhaps “Mister Glass” has always been Elijah’s villain codename. David immediately calls the police and Elijah is sent to an institution for the criminally insane.
