A mother as well as her 3 little girls-- romantic , sensible Evie, as well as youngster of nature Sissy-- inhabit the titular glass structure, which has been entirely sealed off to shield its residents from a dementia-inducing toxic substance called the Shred that's poisoning the air exterior. Fearful of becoming like the shed souls that stray the void outside, the family members maintain an understanding on their past by carrying out spiritual routines. When Bee breaks the guidelines and also allows an injured stranger right into their middle, the family dynamic is shattered forever, as concealed realities upend the impressions the females have actually worked so difficult to shield.