The story begins with several instances of Victor's mother infantilizing him by requesting him to recite the days of the week, wear shorts with stockings, and give his opinion on her children's book illustrations.
After tuning out his mother's ramblings on her new illustration, his mom realizes his disregard, taunts him for acting sound and mocks the shorts she forces him to wear, which is a sore subject for Victor.
He starts crying, and then his mom informs him that her friend, Mrs. Badzerkian, is coming over for tea, and he should recite one of his poems for her.
Later, when entering the kitchen, Victor notices the live terrapin of the title, a small tortoise trying to turn over off its back.
This event pushes Victor over the edge — he believes he heard it scream — and during the night, he butchers his mother with a kitchen knife, only stopping because of tiredness.