David Dunn, a security guard, is the sole survivor of a horrific train crash that kills all the other passengers. Emerging without a single scratch or injury, David struggles with a sense of purpose and questions why he was spared. His marriage to Audrey is failing, and he feels disconnected from his young son, Joseph. David's unremarkable life is thrown into uncertainty as he grapples with the possibility that he might be different somehow – possessing an extraordinary resilience that can't be explained by luck alone.

Elijah Price, an art gallery owner with a rare condition that makes his bones extremely fragile, reaches out to David after hearing about the miraculous survival. Obsessed with comic book heroes, Elijah has developed a theory that if he exists at one extreme of the physical spectrum, there must be someone at the opposite end. He proposes that David might be that person, unbreakable and impervious to harm. Intrigued and skeptical, David embarks on a journey of self-discovery that challenges everything he understands about himself and the world around him.