'finicky tidiness?' "

I was quoting, and I could see that he was not pleased

with my retort.

"Oh, without doubt, Hastings, in some things they

deceive themselves--tant mieux\ They will learn in due

time. Meanwhile we have learnt something, and to

know is to be prepared."

This last was a favourite axiom of his lately; so much

so that I had begun to hate the sound of it.

"We know something, Hastings," he continued.

"Yes, we know something--and that is to the good-but we do not know nearly enough. We must know more."

"In what way?"

Poirot settled himself back in his chair, straightened a box of matches which I had thrown carelessly down on

the table, and assumed an attitude that I knew only too

well. I saw that he was prepared to hold forth at some

length.

"See you, Hastings, we have to contend against four adversaries; that is, against four different personalities. With Number One we have never come into personal

contact--we know him, as it were, only by the impress

of his mind--and in passing, Hastings, I will tell you

that I begin to understand that mind very well--a mind

most subtle and Oriental--every scheme and plot that

we have encountered has emanated from the brain of

Li Chang Yen. Number Two and Number Three are so

powerful, so high up, that they are for the present immune from our attacks. Nevertheless what is their safeguard

is, by a perverse chance, our safeguard also. They

are so much in the limelight that their movements must

be carefully ordered. And so we come to the last member

of the gang--we come to the man known as Number

Four."

Poirot's voice altered a little, as it always did when

speaking of this particular individual.

"Number Two and Number Three are able to succeed,

to go on their way unscathed, owing to their notoriety

and their assured position. Number Four succeeds

for the opposite reason--he succeeds by the way

of obscurity. Who is he? Nobody knows. What does he

look like? Again nobody knows. How many times have

we seen him, you and I? Five times, is it not? And could either of us say truthfully that we could be sure of

recognising him again?"

I was forced to shake my head, as I ran back in my

mind over those five different people who, incredible as it seemed, were one and the same man. The burly

lunatic asylum keeper, the man in the buttoned up overcoat in Paris, James, the footman, the quiet young

medical man in the Yellow Jasmine case, and the Russian

Professor. In no way did any two of these people

resemble each other.

"No," I said hopelessly. "We've nothing to go by whatsoever."

Poirot smiled.

"Do not, I pray of you, give way to such enthusiastic despair. We know one or two things."

"What kind of things?" I asked sceptically.

"We know that he is a man of medium height, and

of medium or fair colouring. If he were a tall man of