M3GAN is a marvel of artificial intelligence, a lifelike doll that's programmed to be a child's greatest companion and a parent's greatest ally. Designed by Gemma, a brilliant roboticist, M3GAN can listen, watch and learn as it plays the role of friend and teacher, playmate and protector. When Gemma becomes the unexpected caretaker of her 8-year-old niece, she decides to give the girl an M3GAN prototype, a decision that leads to unimaginable consequences.

When a lively young family moves in next door, grumpy widower Otto Anderson meets his match in a quick-witted, pregnant woman named Marisol, leading to an unlikely friendship that turns his world upside down.