There is a football game on television that Saturday, so Father is watching it and Christopher doesn't have much to do. He decides to continue his detection and talk to other people on Randolph Street about Wellington. Christopher does not like strangers and it takes a long time for him to get to know people, so doing this requires that he be brave. First, he makes a plan for his part of the street, then makes sure he has his Swiss Army knife in his pocket.
He goes to number 40, right opposite Mrs. Shears, and speaks to Mr. Thompson - who actually turns out to be the brother of the Mr. Thompson who lives there. This brother has no idea who did it and was in Colchester on Thursday. No one answers at number 42 and at number 44 he is greeted by a black woman who is the mother of that household. He asks her if she knows anyone who might want to make Mrs. Shears sad and the woman tells Christopher to ask his father. He responds that his father told him to stay out of other people's business and the woman concurs. At number 43 he speaks to Mr. Wise, who lives with his invalid mother, but Mr. Wise starts laughing at Christopher so he walks away. Christopher does not talk to the people at number 38 since Father says they take drugs and warned him to never talk to them. He proceeds to number 39, which is next to Mrs. Shears' house, and sees Mrs. Alexander in her front garden. She has a dachshund, but it was inside the house. He asks Mrs. Alexander if she knows anything about Wellington's murder but she doesn't. She then tries to start a conversation with Christopher - that is, chatting - and invites him for tea. He refuses since he doesn't go into other people's houses, so instead she offers him squash and a slice of Battenberg cake. Unfortunately, there is yellow in that kind of cake and Christopher doesn't like yellow. So Mrs. Alexander instead offers biscuits and goes into the house. More than six minutes pass and Christopher worries that she might be calling the police, so he walks away.
As he heads home, Christopher is struck with a Chain of Reasoning and concludes that the person who killed the dog would be the one person he knew who didn't like Mrs. Shears, which was Mr. Shears, and that he didn't like Wellington either. Thus, Mr. Shears has become his Prime Suspect. Mr. Shears used to live with Mrs. Shears but left two years ago, which is why she did a lot of cooking for Christopher and Father after Mother died. She sometimes stayed overnight and Christopher liked how she puts thing in order but didn't like when she said things he didn't understand. He doesn't know why Mr. Shears left exactly, though he knows reasons why people get married and subsequently divorce. Christopher decides to try to find out more on Mr. Shears.
Notes - More clues are provided for the second mystery, which Christopher is still not aware of as a mystery. Adultery is one of the reasons he states for people getting divorces, and this turns out to be the key to the mystery of his mother.
Christopher states that all the other children in his school are stupid, though he's not supposed to call them stupid but instead refer to them as having learning difficulties or having special needs. This in itself is stupid, because everybody has learning difficulties, depending on the subject, and everyone has special needs of one kind or another. Siobhan insists that these terms should be used because otherwise the children at the school will be called nasty words. Christopher finds this odd, since other children use "Special Needs!" to taunt students in his school as well. Christopher is going to prove that he's not stupid by taking his A levels in math and getting an A grade. Mrs. Gascoyne, his school's headmistress, didn't want to do this but Father convinced her. After this first test Christopher plans to take A-level further maths and physics; and from there, he will go to university, get a degree, find a job, and get married.
Notes - Christopher again points out the absurdities of language, this time regarding the use of politically correct terms for the mentally challenged (which is itself a politically correct term). He describes his plans for life and it's worth noting how it's a typical aspiration. The only unusual aspect is his desire to eventually marry, emphasizing companionship and being cared for, but not considering love or romance.
Christopher used to believe his parents would divorce because they argued often when he was younger due to the stress of looking after someone with Behavioral Problems. However, he doesn't have as many problems as he does now. He lists from A to R some of the Behavioral Problems he has and speaks of how his parents would shout at him when he didn't behave.
Notes - The list of Behavioral Problems is idiosyncratic, ranging very specific as well as very general. One point, "P. Hating France," is mildly amusing because of a traditional disdain held between the two countries. However, it is comprehensible in Christopher's case as he does not like unfamiliar experiences and details the discomfort of trips to France with his parents.