"Average Waves in Unprotected Waters" begins at first light on the day Bet Blevins, the story's protagonist, is to institutionalize her mentally handicapped son, Arnold. At the age of nine, Arnold has become too difficult for Bet to manage. In the shabby, one-room apartment, Bet wonders, as she prepares Arnold's things and dresses him one last time, if he understands what is happening and if she is truly making the right decision. As they leave the crumbling apartment building, Mrs. Puckett, a kindly neighbor who is crying, stops Bet and gives her cookies for Arnold, but he runs off without acknowledging the woman who has baby-sat for him since his birth.

After taking a bus from their apartment, Bet and Arnold arrive at the train station. Bet has purchased gum, which she gives to a nervous Arnold. As the train leaves, he becomes calmer and falls...