Unlike in many other depictions, it is seen as a prolonged war, which does not destroy all civilization at once - but extensive use of nuclear bombs causes radiation poisoning and has led to a rash of mutated babies (it is implied that only a small fraction of pregnancies result in the birth of normal children).

In these letters we learn of Margaret's fears of giving birth to a mutant, disturbing tales of infanticide by the fathers of deformed babies, her successful labor, and the rapid development of the newborn.

The daughter, named Henrietta, is extremely precocious, speaking in complete sentences by the time she first meets her father at the age of ten months.

When Hank returns home, he discovers that his daughter has no arms or legs, and that his wife is in such strong denial that she does not realize she has given birth to a mutant.

"That Only a Mother" falls into a category of mid-century science fiction writing often referred to as the "housewife heroine" story, works that deal explicitly with domestic themes and the experiences of women.