The sick child of the title is ten-year-old Jean. His legs are semiparalyzed, and he is extremely weak and emaciated, but pallor has given him an ethereal beauty. From the beginning of the story, the reader is led to expect that he will die. The description of the sickroom suggests a prosperous and cultured background.

The first part of the story establishes a delicate relationship between the sick child and his widowed mother, whom he calls “Madame Mamma.” He tries to conceal his pain from her; she tries to conceal her anxiety from him. They both know that they are deceiving each other in their determination to protect each other from the truth.

There is another and more compelling reason—which becomes the central part of the narrative—for Jean to keep his mother distanced from his real thoughts. He is conserving his daytime energy so that at night he can indulge in fantastic journeys of the imagination, which have become the reality of his sickbed existence. To conceal this reality from his mother, he has adopted a slightly mocking approach toward her, which gives him some power over her. His long-drawn-out illness has made him hyperreactive to sensations, with all the senses intermingled: He can hear smells, taste sounds, smell textures. He has become intensely involved with words and uses a secret vocabulary to describe the people and the everyday things around him.

His nighttime journeys are often sparked by his power to animate the everyday objects or sensations within his bedroom. The scent of lavender, sprayed by his mother, becomes a cloud of fragrance on which he can ride through the skylight into the world beyond. He can fly freely and flowingly, above fields and pastures, with complete control over his adventures and over everything within them. He laughs as he flies, although he never laughs in bed. He dreads landing back in bed, for he often bumps himself on the iron frame and wakes up in pain. He denies the pain that he feels, however, when Madame Mamma questions him.

Besides his mother, the most frequent visitor to the sickroom is the maid Angelina, whom he has rechristened “Mandora.” He loves Mandora because she radiates a profusion of colors, sounds, and feelings. His least favorite visitor is the doctor, whom he finds patronizing and cold. He regards the children who visit him—his cousin Charles, with his scratched knees and hobnail boots, and a little girl who talks about her ballet lessons—as tolerable daytime irritations, for he knows that when night falls, he can find true enjoyment by flying away on one of his adventures again.

One night, Jean’s voyage ends when he comes down to earth and hears some words that he cannot quite grasp. The reader understands them as “crisis” and “poliomyelitis.” Jean hears them in the shape of people’s names and conjures up visions of their owners.

In a protracted period of delirium, the boy’s fantasies take on a different and more disturbing texture. Inanimate objects, which were previously at his beck and call, begin to defy him. He finds himself in the grip of unfamiliar presences and sensations. He wants to cry out to Madame Mamma, but an invisible wall separates him from her.

As the fever mounts, strange feelings assail his legs, as if they are being assaulted by ants; menacing forces attack him with burning heat and icy cold. A sudden calm and sadness indicates to the reader that Jean is close to death. His hallucinations become increasingly disoriented. Occasionally, consciousness breaks through as he hears, in distorted form, the sound of bedside voices.

Still struggling to take command of the situation, he at last succumbs to tears. He feels the touch of soft flesh and hair and falls asleep with the knowledge that he is nestling on his mother’s shoulder. When he awakens, he has regained enough of his old self to greet her with one of his slightly mocking comments.

In a state of blurred consciousness, he politely asks Madame Mamma to scratch his calves as the “ants” are plaguing him again. This indication that he has regained some feelings in his legs causes excitement among the adults at his bedside, but he becomes conscious of a hateful presence among them and tries to use his powers to abolish it. He discovers that it is the doctor and that the doctor’s eyes are filled with tears.

The following weeks bring a muddled and lethargic succession of short and long sleeps, sudden awakenings, and small treats of jelly and vanilla milk. As the “ants” become increasingly active and his appetite returns, Jean’s powers decrease until he is no longer able to conjure up his cherished visions. Inanimate objects refuse to obey him. He can no longer fly. He has defeated death. He is on the mend and is sleeping well at night, but the nights are without marvels. The final word of the final sentence indicates that, contrary to the reader’s expectations, Jean is disappointed.