Almost dying in the delivery room, Alice Leiber gives birth to a healthy baby boy. Instead of being filled with joy, though, Alice is horrified because she is convinced that her baby is trying to kill her. At first, her husband, David, refuses to believe that anything is wrong. Later, however, he is called home from a business trip because his wife is near death because of pneumonia. He is forced to give second thoughts to his wife's fears when she vows that the child made her ill by crying so loudly through the night that she could not get proper rest. She insists that their child almost succeeded in ending her life.
One night when the baby will not stop crying, David goes downstairs for the baby's bottle. In the dark, he trips on the baby's doll and nearly plunges headfirst down the stairs. Luckily, he grabs the banister. Alice, however, is not so fortunate, because David discovers her the following day lying twisted and dead at the foot of the stairs. She, too, tripped over the baby's doll. Now his wife's accusations concerning their son return to him. He finally accepts the idea that his son is the "small assassin" who placed the doll at the head of the stairs each time. He becomes hysterical. Dr. Jeffers sedates David and puts him to bed, assured that he will not awaken until morning. When the doctor gets no answer at Leiber's home the next day, however, he steps inside and, smelling gas, races to David's room. There he finds David still lying in bed, but dead. Now Dr. Jeffers begins to believe in the baby's evil actions and goes in search of the baby with a scalpel in his hand.
"The Small Assassin" is a good illustration of Bradbury's technique of putting a little twist on reality. Here there is the intrusion of a baby named "Lucifer" into the previously normal life of David and Alice Leiber. At first, the child seems harmless enough, and the reader has a tendency to judge Alice as the "strange" character because of her fantasy concerning the child. Before long, however, the reader agrees with Alice that the baby's actions are menacing. Too often, the baby's face is red and his lips are moist. The norm has been upset. Ultimately, both parents are murdered, and Dr. Jeffers' determination to perform terminal surgery on the child adds a deft touch of horror. The reader is left to decide whether or not Lucifer was indeed destroyed.