What is the climax in the novel, The Water Cure?

When the sisters all take part in the harrassment and bullying of Gwil, their treatment becomes unbearable, and he runs away. Later, the girls discover his body in the forest, where he had been stung to death by hornets. Gwil's death sets the climax of the novel in motion, because Grace believes that Llew will kill them in response. Thus they must kill James and Llew to ensure their own safety.