The play opens with Christopher discovering the dead dog, which belongs to SelectMr ShearsMrs ShearsRhodri.
Christopher is arrested by a policeman because Selecthe hits himhe swears at himhe runs away from him.
Mrs Alexander tells Christopher that his mum isn't dead, she left because Selectshe was scared of his fathershe killed the dogshe was having an affair with Mr Shears.
Christopher discovers the letters sent by his mother. He finds out that she now lives in SelectSwindonLondonSutton.
When Christopher can't buy a map to find the train station, he finds it by Selectasking for directionsguessing where it ismoving in a spiral.
The voice of Siobhan helps Christopher find the platform his train is on by telling him to Selectimagine he is drumming a rhythmbreathe and count to tenask for help.
Christopher gets onto the train track of the underground to pick up his Selectpen knifemaprat, Toby.
After Christopher has arrived at his mother's flat, he decides he needs to go back to Swindon to Selectsay sorry to his fathersit his maths A-leveltake Toby back.
Christopher and his mother leave London to return to Swindon, they take Selectthe busthe trainMr Shears' car.
At the end of the play, Christopher explains how he answered the maths question, he used SelectFermat's last theoremPythagoras' theoremPrime number theorem.