Broken Bond, A by Nicholas Carter

Nick Carter is a fictional private detective who first appeared in 1886 in dime store novels. Over the years, different authors, all taking the nom de plume Nicholas Carter, have penned stories featuring "America's greatest private detective". This tale opens in South America, with a lone man lying in wait in the mountains. He lets a caravan of peasants pass. Ten minutes later, the sound of a horse's hooves signal the arrival of his quarry. Who is the man and why is he trying to shoot his victim?