In a few short sentences he explained to the inspector the facts
about the letter and the cipher. MacDonald sat with his chin on
his hands and his great sandy eyebrows bunched into a yellow
tangle.

"I was going down to Birlstone this morning," said he. "I had
come to ask you if you cared to come with me--you and your friend
here. But from what you say we might perhaps be doing better
work in London."

"I rather think not," said Holmes.

"Hang it all, Mr. Holmes!" cried the inspector. "The papers will
be full of the Birlstone mystery in a day or two; but where's the
mystery if there is a man in London who prophesied the crime
before ever it occurred? We have only to lay our hands on that
man, and the rest will follow."

"No doubt, Mr. Mac. But how do you propose to lay your hands on
the so-called Porlock?"

MacDonald turned over the letter which Holmes had handed him.
"Posted in Camberwell--that doesn't help us much. Name, you say,
is assumed. Not much to go on, certainly. Didn't you say that
you have sent him money?"

"Twice."

"And how?"