Sergeant Hobson of the Western Australia Police Force started his shift at five in March 1917. As he rode his bicycle along Beaufort Street, the early morning light struggled to break through the heavy clouds. Ka-lop, ka-lop, ka-lop, ka-lop. A fast-moving horse put him on alert. Ka-lop, ka-lop, ka-lop. Where was it coming from? Ka-lop,…