''Tragedy on the Line'' by John Rhode, first published in 1931.
The wealthy Gervase Wickenden is found dead on the railway line near Upton Bishop's station. Decapitated it is at first assumed he was killed by a train, until a bullet is discovered in a nearby tree. Added to this was the suspicious fact that he had changed his will only two days before, and both the old and the new version are now missing.
