Porlock - the Mystery of the Thirteen Steps: a "spot-the-difference" murder mystery

It is 1904, and every day the coaches plying between Lynmouth and Minehead scramble their way up and slither their way down the 1 in 4 gradient of Porlock Hill, the most feared hill in all of England. It takes six sturdy horses to drag a laden carriage to the top. There, the leading pair are detached and led back down into the village by a boy, a boy who knows how lucky he is to have been given such a responsible job at such a young age. But on this day in May, on his return journey with the tired horses Pug and Delia, he spots what looks like a sheep sheltering on the hillside. But as he gets closer, his heart races as he becomes aware… it is not a sheep… it is a white dress…