“A Small, Good Thing” begins on a Saturday afternoon in an unnamed American city. Ann Weiss, a young mother, drives to the shopping center and orders a chocolate cake for her son Scotty's eighth birthday, which will be on Monday. The baker is a taciturn man, and Ann does not take to him. He promises the cake will be ready on Monday morning.

On Monday morning, Scotty is walking to school with another boy when he steps off the curb at an intersection and is knocked down by a car. The car stops but when Scotty gets to his feet and looks as if he is all right, the car leaves the scene. Scotty walks home but then collapses on the sofa and loses consciousness. He is taken to the hospital, where he is diagnosed with mild concussion and shock. He is in a deep...