Christopher Boone discovers Wellington the poodle dead on Mrs. Shears's lawn, impaled by a garden fork.

Police officers arrive, question Christopher, and arrest him after he strikes an officer who tries to lift him.

Christopher's father arrives at the police station and secures Christopher's release into his custody.

Christopher decides to investigate Wellington's murder and begins questioning the neighbors on his street.

Christopher's father discovers the investigation is continuing and forces Christopher to promise to stop.

Neighbor Mrs. Alexander reveals that Christopher's mother and Mr. Shears had a sexual affair.

Christopher's father reads the detective journal, grabs Christopher in anger, and a physical fight breaks out.

Christopher searches his father's bedroom and discovers a bundle of his mother's letters hidden beneath the journal box.

Christopher's father tearfully confesses he lied about Christopher's mother dying — she left with Roger Shears.

Christopher's father confesses he killed Wellington after Mrs. Shears kicked him out and the dog attacked him.

Fearing his father is dangerous, Christopher hides overnight in the backyard and plans to travel to London alone.

Christopher navigates Swindon's train station alone, buys a ticket, and boards a train bound for London.

Christopher arrives at his mother's Willesden flat and waits outside in the rain until she comes home.

Christopher's mother decides to leave Roger Shears behind and moves back to Swindon with Christopher.

Christopher sits his A-level math exams and receives an A grade, despite exhaustion and disrupted preparation.

Christopher Boone's discovery of a murdered dog sets off an investigation that pulls him into a web of family secrets his father has carefully hidden. As he questions neighbors and defies his father's orders to stop, he uncovers the truth that his mother never died but left for London with a neighbor. Betrayed and frightened, Christopher undertakes a terrifying solo journey across England to find her. He reunites with his mother, who must choose between her new life and her son, ultimately choosing Christopher. Despite the chaos, Christopher sits his A-level math exams and earns a top grade, proving to himself that he can achieve anything.

The headline events of Christopher's investigation and journey.

Mrs. Shears runs out shouting at Christopher for holding Wellington's body; Christopher curls up on her front lawn.

Police place Christopher in a holding cell, where he methodically records every detail of the small cube-shaped room.

Christopher sneaks into Mrs. Shears's backyard shed and notes the garden fork belongs to a matching set of tools.

Siobhan suggests Christopher write a book about his investigation, starting the journal that becomes the novel.

Christopher's father argues with headmistress Mrs. Gascoyne and successfully arranges for Christopher to sit the A-level math exam.

Christopher visits Mrs. Alexander, who goes inside to fetch tea, and Christopher nervously walks away before she returns.

Christopher's father apologizes for the fight and takes Christopher on a rainy-day trip to the zoo.

Siobhan notices a bruise on Christopher's face at school and asks whether he is afraid to go home.

Christopher breaks back into his own house, packs a bag with clothes and food, and takes his father's bank card.

Christopher spots his father's work van near school, vomits from fear, then pushes on until he locates the train station.

A policeman at Swindon station helps Christopher use a cash machine and guides him to the ticket counter.

Christopher hides on a luggage shelf inside a train toilet to evade a policeman trying to remove him at the next stop.

Christopher jumps onto Underground tracks to rescue Toby the rat and is dragged back to the platform before a train arrives.

Roger Shears scolds Christopher in the London flat; Christopher's mother packs their bags and announces they are leaving.

Christopher's father gives Christopher a golden retriever puppy as a gesture of reconciliation.

While Christopher's detective work drives the main story, a series of quieter but significant moments shape the world around him. His teacher Siobhan encourages him to write a book, creating the very narrative the reader holds, while his father arranges for Christopher to sit a high-stakes math exam over the headmistress's objections. After the violent fight with his father, a zoo trip marks a fragile peace before everything unravels again. Christopher's solo journey to London is filled with harrowing practical challenges — spotting his father's van, navigating the Underground, and rescuing his rat from the tracks. The story resolves with a puppy gift signaling the slow rebuilding of trust between father and son.

The supporting scenes that shape Christopher's world and journey.

Christopher reasons that his promise to stop detecting contains loopholes and quietly continues his investigation.

Christopher deduces that Mr. Shears is his prime suspect, reasoning that someone wanted to make Mrs. Shears miserable.

Christopher's father strikes the dinner table in fury when Christopher announces Mr. Shears as his prime suspect.

Christopher regains consciousness after the fight and watches his father carry the journal outside to throw it away.

Christopher searches his father's bedroom and finds the detective journal hidden in a shirt box inside a wardrobe drawer.

Christopher reads the first of his mother's hidden letters and realizes she is alive and living in London with Roger Shears.

Christopher reads more of his mother's letters and learns she left partly because she felt unable to cope with raising him.

Christopher's father confesses to killing Wellington; Christopher screams and his father retreats from the room.

After hiding overnight, Christopher knocks on Mrs. Shears's door hoping she will shelter him, but she does not answer.

Christopher watches 47 Underground passengers to decode the ticketing system before buying his own ticket to Willesden.

Christopher's mother arrives home with Roger Shears to find Christopher standing wet and shivering outside her front door.

Christopher's father arrives at the London flat in the middle of the night and demands to see his son.

A policeman arrives at the London flat and escorts Christopher's father away after the late-night confrontation.

Christopher's mother cancels his A-level exam booking without his agreement; Christopher screams in protest.

Christopher learns he earned an A grade and declares that, having solved the mystery and written a book, he can do anything.

Beneath the surface of Christopher's investigation lies a series of pivotal moments where his understanding of the world shifts dramatically. His private reasoning about loopholes and suspects slowly edges him toward truths his father is desperate to conceal, culminating in the shattering discovery that his mother is alive. Each revelation — the first letter, the later confessions — forces Christopher to reassess everything he thought was safe and certain. His escape to London is itself a turning point, as he encounters obstacles that demand courage and adaptability he never knew he possessed. By the end, armed with an A grade and a new puppy, Christopher arrives at the most important revelation of all: that he is capable of anything.