The plot of This Sunday is divided into five parts, presented through two different narrative voices. The first narrator, one of the grandchildren of Chepa, remembers, many years later, the weekends spent as a child at the house of his grandparents. His narrative includes the parts entitled “In the Fishbowl,” “Legitimate Games,” and “Sunday Night.” The second voice is that of a third-person narrator who presents certain aspects of the life of Alvaro and Chepa unknown to the grandchild, and who relates the chapters entitled “Part One” and “Part Two.”
This section of the story starts when Alvaro is a high school student. While his family is vacationing at a nearby resort, he must stay at home to prepare for exams. In the solitude of the house, sexual relations develop between Alvaro and Violeta, the maid in charge of taking care of him. Years later, Alvaro marries Chepa, but the marriage fails very soon because of temperamental incompatibilities. Both Alvaro and Chepa immerse themselves in selfish existences, isolated from each other, each of them solely concerned with his or her own interests. Alvaro takes refuge in himself, and Chepa hides her sexual frustrations behind charitable concerns for others. As the years pass, their marriage is reduced to a routine governed by the rules imposed by Chepa.
In a visit to the penitentiary, Chepa meets Maya, a brutal murderer. From the very first moment, she experiences a dark and irresistible attraction toward the convict and decides to obtain his freedom. Once she has achieved her goal, Chepa projects on Maya all her secret frustrations, hoping to exert absolute dominion over him, as she does with all those who surround her. Maya cannot cope with this type of life, and after a turbulent relationship of deceit and falsehood, he disappears.
The novel begins on a Sunday morning (its title alludes to this particular day) when Maya reappears several years later, seeking help from Chepa. Alvaro, however, impedes their meeting and, in doing so, sets in motion a fatal sequence of events.
The bulk of the novel concentrates on the torturous relationship between Chepa and Maya. Expanding from this point, the novel illuminates the distorted world of human relations that envelops all the characters, and its unavoidable breakdown.