This is the beginning of the book when Christopher finds Wellington dead in Mrs. Shear yard. There was a garden fork sticking out of the dog." Haddon says on page1 of Curious Incident.
This is when Christopher and Mrs. Alexander were in the park and she told him that his mom was cheating on his dad with Mr. Shears. "And she said, 'No, Christopher. I'm not sure that you do. I mean that they were very good friends." Haddon say on page 60 of Curious Incident.
This is when Christopher finds the letters from his mom that his dad was hiding from him. "I counted the letters. There were 43 of them. They were all addressed to me in the same handwriting." -Haddon page 104 of Curious Incident.
This is when Christopher is at the train station and is trying to get to his mother but the police officer stops him.
This is when Christopher and his mother find each other and shes telling him that he can stay with her and Mr. Shears doesn't want him to stay.
This is at the end when his mother and father tell him that they need to try to make it work as a family so they can stay together.