The Valley of Fear

From the text:

In the first place, I may tell you that Moriarty rules with a rod of iron over his people. His discipline is tremendous. There is only one punishment in his code. It is death. Now we might suppose that this murdered man—this Douglas whose approaching fate was known by one of the arch-criminal’s subordinates—had in some way betrayed the chief. His punishment followed, and would be known to all—if only to put the fear of death into them.”