Heartwarming / The Curious Incident of the Dog in the Night-time
Christopher reconnecting with his father after everything that's happened. It was clear that there was a real risk that the estrangement might have been permanent, and his father was all too aware of that. Even though Christopher can't recognise the signs, it is clear to the reader how much it means to him when Christopher acknowledges his presence again.
Christopher's father getting him a new puppy near the end of the story. This troper was watching the theatrical version, and the entire theatre d'awwed for at least two minutes when they brought the puppy on. More than one person in the audience was crying.