Sidney Bridge upside down

"There was an old man who lived on the edge of the world and he had a horse called Sydney Bridge Upside Down." A captivating opening line of a gothic novel superficially about a boy in rural New Zealand in the 1930s. However the tone and voice of the narrative changes from the original boyish perspective of the narrator, to something darker - even unhinged. The plot is simple on the surface but its undercurrents disturb.