complained, Sir
Hilary, that I talked like a detective out of a book. This kind of thing
makes me feel like one--except that, in this case, I cannot claim much
credit. I only used common sense and perseverance."

"Let us have it," said Grell. He was beginning to be his own masterful
self.

"Very well. It has all been a matter of organisation. You will remember,
that in dealing with an intricate case no man is at his best working
alone. However able or brilliant a detective is, he cannot
systematically bring off successful coups single-handed--outside a
novel. He is a wheel in a machine. Or perhaps, a better way to put it
would be to say, he is a unit in an army. He is almost helpless alone.

"There are many people who believe that a detective's work is a kind of
mental sleight of hand. By some means, he picks up a trivial clue which
inevitably leads, by some magical process, to the solution of the
mystery. I do not say that deductions are not helpful, but they are not
all. A great writer once compared the science of detection to a game of
cards, and the comparison is very accurate. A good player can judge,
with reasonable certainty, the cards in the hands of each of his
opponents. But he can never be absolutely certain--especially when he is
unacquainted with his opponents' methods of play.

"Detection can never be reduced to a mathematical certainty until you
level human nature, so that every person in the same set of
circumstances will act in exactly the same way. Like doctors, we have to
diagnose from circumstances--and even the greatest doctors are wrong at
times. Specialist knowledge has often to be called in.

"When this case commenced, specialist knowledge had to be enlisted to
fix our facts--and the one general difficulty which arose as always, was
that we did not know which facts might prove important. As an instance,
I may say that the finger-prints on the dagger were wholly misleading,
and might have brought about a miscarriage of justice.

"It was necessary that we should collect every fact we could about the
murder, whether great or small. That was one phase for the investigation
where organisation was necessary. A man working alone would have taken
months, perhaps years, in this preliminary work. Then luck favoured us.
Our records--collected, of course, by organisation--contained a portrait
of a man strikingly like you"--he nodded to Grell--"and a comparison of
finger-prints told us that the dead ma