Christopher has one of his favorite dreams. In it, nearly everyone on earth is dead, and all that are left are special people like himself who want to be alone and don't look in other people's faces. In this dream, Christopher can go anywhere in the world and not be bothered. He goes to Father's house and it is quiet even at mid-day; he can go into other people's houses and play detective and does whatever he wishes, since you can do anything you want in a dream. He then finds someone's car keys and drives the car into the sea. He watches the surf afterwards then gets dry clothes and returns home to Father's house, which is now his. This dream makes him happy.
Notes - Again, this dream emphasizes how different Christopher is from others. The fact that he claims Father's house as his own shows how he is most comfortable there, that this is his true home.
The next morning during breakfast, Mr. Shears and Mother argue over how long her can stay with them. Mother takes the day off from work and takes Christopher shopping for clothes, but he grows frightened and screams so Mother takes him home. She goes shopping on her own and returns with new pajamas for Christopher. He tells her he has to go back to Swindon to take his maths A level exams, which surprises her. She doesn't know if returning to Swindon would be possible, which alarms Christopher. That night, he could not see the stars because of light pollution; when he finds he cannot sleep and at 2:07 a.m. he goes outside and sits between a skip and a Ford Transit van. He hears Mother calling for him and when he goes to her she warns him against going outside on his own again, as it's too dangerous in London.
The next day he spends indoors watching videos and the next day the office where Mother works called and told her she was replaced. Christopher again reminds Mother about going to Swindon for his A level, but she says it can be postponed. The next morning he looks out the window to count the cars but there are too many for him to be able to decide if it was a Good Day or Black Day - the system didn't work in London. That afternoon they go to Hampstead Heath to watch planes from Heathrow Airport and Mother tells Christopher that she spoke to Mrs. Gascoyne and delayed the exam until next year. Christopher is upset and screams, and they return home. Mr. Shears brought library books on math and science for Christopher, but they were for children so he didn't read them. Mother and Mrs. Shears ague and Christopher drowns them out by setting his radio to white noise.
Monday night, a drunk Mr. Shears wakes up Christopher to harass him verbally. The next day, Mother packs her clothes and takes Mr. Shears' car to return with Christopher and Toby back to Swindon. They go to Father's house and when Father comes home Mother tells him to stay with Rhodri until she finds a new place for herself and Christopher. Christopher continues to bring up his maths A level exams and Mother apologizes for this. The next day Mother drives Christopher to work and Mrs. Shears insults her. Siobhan meets with Mother and then arranges for Christopher to take his A level after all. She asks him if this is what he really wants to do and he isn't sure because he isn't able to think as clearly about maths as before. Still, he decides to take the test and that afternoon takes the first part while Reverend Peters serves as invigilator, as was originally planned.
Christopher is at first violently frustrated at Paper 1 but calms himself down, managing to take the test. The next day he takes Paper 2 and that evening Mr. Shears comes to take back his car. The following day Christopher takes Paper 3 and has a favorite question: he wants to write out how he answered this question but Siobhan told him it wasn't interesting to most people and he can include it in an Appendix. Christopher must wait to hear the results of his exams and is not sure of how well he did. The night of Paper 3, Father comes to the house to ask how the exam went. Christopher tells him and Father says thank you.
The next week Father tells Mother she has to move out of the house. Christopher asks her if Father will be arrested for killing Wellington but she says that the police can only do so if Mrs. Shears will press charges - which she won't. Mother gets a job and has pills prescribed to stop her from feeling sad. She and Christopher move to a room in a big house. He continues to wait for the exam results; mother gives him a wooden puzzle and they paint the room they now live in. Because of Mother's work, Christopher has to stay at Father's house between 3:49 p.m. and 5:30 p.m. To keep himself safe, Christopher pushes the bed against the door; Father sometimes talks to him through the door. Toby dies because he was old for a rat, so Christopher and Mother bury him in a plastic pot since the place they live has no garden. Christopher solves the puzzle that Mother gave him.
One day, Father asks to speak to Christopher; he refuses, but Mother says its OK. Father says it hurts having Christopher refusing to talk to him and wants Christopher to learn to trust him again, no matter how long it takes. He calls this a project that they can work on together, to spend more time together to rebuild trust. He then brings in a cardboard box with a two-month old golden retriever inside. Christopher names the dog Sandy. Christopher finally gets the results from his maths A level and it is an A grade, which makes him happy. When Mother gets the flu, Christopher spends three days with Father but it's okay because he sleeps with Sandy keeping guard. Father begins a vegetable patch in the garden and Christopher helps with this.
Mother helps him get a book for A-level further maths, which he will take next year. He knows he will get an A grade, as he will in A-level physics the year after that. When this happens, he will go to university in another town - not London - and take Sandy with him, and wind up a scientist. He knows he can do this because he went to London on his own, solved the mystery of Who Killed Wellington?, found his mother, was brave, and wrote this book - which means he can do anything.
Notes - The only time we see Christopher in an aggressively violent mood - as opposed to defensively to protect himself - is at the start of his exam, when he isn't sure about his math skills. This is because his main source of stability, the logical way he looks at the world and filters its information, isn't as strong as it could be when he needs it most. The book ends on a realistically hopeful note, as Ed Boone slowly regains the trust of his son.
This is the solution to Christopher's favorite exam question from A-level maths.
Notes - By ending with an actual mathematical problem, we not only see its importance in Christopher's life but are given a symbolic restoration of order in his world.