A baby is born in West Philadelphia, and that child is Elijah Price (Samuel L. Jackson). From the start, Elijah's life is marked by fragility, as he is born with brittle bones, resulting in broken arms and legs. As he grows up, he endures relentless torment at school and earns the nickname Mr. Glass from his classmates. Despite these challenges, Elijah channels his passion into adulthood by running a high-end comic book art gallery, showcasing original superhero artwork.
On the other side of town, David Dunn (Bruce Willis) works as a security guard at a local college stadium. His personal life is in disarray; his marriage is on the rocks, and Audrey Dunn (later revealed to be portrayed by Robin Wright Penn) sleeps in their son’s room while he occupies his own.
One fateful day, while returning from a job interview in New York, David finds himself in a catastrophic train derailment that claims the lives of all passengers—except him. Miraculously, not a single scratch adorns his body. Post-memorial service for the deceased, David discovers a mysterious note on his car from a comic book store called Limited Editions, which intriguingly poses the question, "Have you ever been sick?" This leads David to visit the gallery where he ultimately encounters Elijah.
In their first meeting, Elijah shares his compelling theory with David—that if he can be so weak and susceptible to injury, there must exist a person with the opposite abilities. He has dedicated years to uncovering a sole survivor of various tragedies; and, at last, he believes he’s found one in David. Initially skeptical, David dismisses Elijah’s theories as sheer lunacy.
However, a strange encounter prompts David to acknowledge his unseen abilities. After instinctively sensing a crime about to unfold while bumping into a stranger, he discovers Elijah has correctly identified David's hidden talent. As David practices weightlifting at home, he marvels at his newfound strength, which his son eagerly believes is proof of his father's heroism.
Through their bond, the audience learns more about David’s past, including a haunting memory of drowning as a child, suggesting he too has vulnerabilities. Elijah pushes David to confront his potential role as a protector; yet, David is still apprehensive about his ‘superhero’ status.
After a harrowing incident, where David foils a violent crime while in his rain poncho—an attire evoking the aesthetics of a superhero—he slowly begins to embrace this new identity. He later returns home, subtly revealing to his son that he was the mystery hero who saved two young girls, affirming the superhero speculation his son has about him.
As the plot unfolds, David pays a visit to Elijah's gallery, only to discover a dark truth hidden beneath the surface. After shaking hands, he experiences a series of chilling visions confirming that Elijah is not just a frail man but rather the orchestrator of countless disasters—his misdeeds cloaked under the guise of seeking a hero. Elijah, with his menacing declaration of being Mr. Glass, unravels a deep-seated rivalry, marking David as the ultimate challenge he has long awaited.
In the sobering aftermath, a message appears on the screen, indicating that David, grasping the weight of Elijah’s schemes, contacts the authorities, leading to Elijah's confinement in a mental institution—a fitting conclusion to the battle between the two intricately linked destinies.
