The tension begins when Mr. Carr confronts Alfred about stealing items from the store. Initially, the tension is solely between Carr and Alfred, although the psychological tension is described from Alfred's perspective. He tensely waits for his mother. He does not look forward to that confrontation but the tension increases because he hopes she arrives before Mr. Carr can locate a police officer.
So, the tension is first, between Alfred and Mr. Carr. Then the tension is within Alfred himself as he anticipates what will happen to him.
But the more significant and more dramatic tension is between Alfred and his mother. He and Mr. Carr expect her to come in ashamed or angry. Instead, she is quiet and polite and this, ironically, allows her to take command of the situation. By the end of the encounter, it is Mr. Carr, not Alfred or his mother, who is apologizing.
The tension increases as Alfred and his mother walk silently home. But, again this tension is not just between the two of them; this story shows Alfred's psychological struggle with understanding how and why his mother acted so generously. By the end of the story, we learn that she was putting on an act in order to protect Alfred. He notices her trembling and concludes that this is the first time he really considers her role as his mother. Alfred, perhaps for the first time, unselfishly understands who she is, who she has been; thus, he knows "all the years of her life." At this moment, the tension remains in Alfred's mother; she will always worry about her children. Alfred matures in this moment. He even expresses empathy for his mother (in thought). There is a shift from tense uncertainty (in Alfred's mind) to familial understanding. That is to say, the reader is left with the possibility that Alfred's epiphany allows him to understand his mother's intensity, her trembling.
All the emotions and tension are inferred because this story is told from the point of view of a third person, partially omniscient narrator. The narrator gives us insight about what Alfred's thinking but we have no clues as to what Mr. Carr or Mrs. Higgins is thinking. The reader, like Alfred, is left to guess what the other two are thinking. This stylistic technique of withholding information increases the tension .