Climax
The climax of this novel would have to be the moment when Ed reveals that he was the one to kill Wellington. This is true because all of the events that lead to the conclusion all sparked from that one moment when Christopher is told that his father was the one to kill the Shears family's dog. It is the moment that answers the book, because the main plot is discovering who killed Wellington, and that has been solved now. Also, it is the moment in the novel that answers most, if not all of the questions that readers may have while reading the book up to this point.