studied both the exterior and the flap.

"It is Porlock's writing," said he thoughtfully. "I can hardly
doubt that it is Porlock's writing, though I have seen it only
twice before. The Greek e with the peculiar top flourish is
distinctive. But if it is Porlock, then it must be something of
the very first importance."

He was speaking to himself rather than to me; but my vexation
disappeared in the interest which the words awakened.

"Who then is Porlock?" I asked.

"Porlock, Watson, is a nom-de-plume, a mere identification mark;
but behind it lies a shifty and evasive personality. In a former
letter he frankly informed me that the name was not his own, and
defied me ever to trace him among the teeming millions of this
great city. Porlock is important, not for himself, but for the
great man with whom he is in touch. Picture to yourself the
pilot fish with the shark, the jackal with the lion--anything
that is insignificant in companionship with what is formidable:
not only formidable, Watson, but sinister--in the highest degree
sinister. That is where he comes within my purview. You have
heard me speak of Professor Moriarty?"

"The famous scientific criminal, as famous among crooks as--"

"My blushes, Watson!" Holmes murmured in a deprecating voice.

"I was about to say, as he is unknown to the public."