And to this day that disappearance remains a mystery unsurmountable.  One morning a week later, after Mead and O’Reilly had gone, when the new master of the ranch arose it was to find a wicked-looking mouse-coloured cayuse standing motionless by the stable door.  Upon him was neither saddle nor bridle nor mark of any kind.  Somewhere out on that limitless waste he had been released, and, true to an unerring homing instinct, he had returned; but from where no man could do more than speculate.  He could not speak, and his rider was seen no more.  Somewhere out there amid that same solitude a thing of mystery had come to pass; but what it was only Nature and Nature’s God, who alone were witness, could ever know.