M3GAN is a marvel of artificial intelligence, a life-like doll programmed to be a child's greatest companion and a parent's greatest ally. Designed by brilliant toy-company roboticist Gemma (Get Out's Allison Williams), M3GAN can listen and watch and learn as she becomes friend and teacher, playmate and protector, for the child she is bonded to.

When Gemma suddenly becomes the caretaker of her orphaned 8-year-old niece, Cady (Violet McGraw, The Haunting of Hill House), Gemma's unsure and unprepared to be a parent. Under intense pressure at work, Gemma decides to pair her M3GAN prototype with Cady in an attempt to resolve both problems – a decision that will have unimaginable consequences.