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 helping his father plant the vegetable garden is sweet, especially since it's a far cry from the former screaming whenever the latter was in the room, showing that their relationship is slowly healing.
Christopher's father getting him a new puppy near the end of the story.