"Do you want to die?!" seven-year-old Samuel inquires of his exhausted single mother, Amelia. She wonders if his question is a threat or a warning. After dealing with Samuel's frantic tantrums his entire life, Amelia suspects her son has begun directing his violent misbehavior toward her. However, after a mysterious and foreboding children's book called Mister Babadook mysteriously finds its way to Samuel's shelf, Amelia must decide if her son is deranged or if there truly is a bogeyman hiding in the shadows around them at night.