“Education never ends, Watson. It is a series of lessons with the greatest for the last. This is an instructive case. There is neither money nor credit in it, and yet one would wish to tidy it up. When dusk comes we should find ourselves one stage advanced in our investigation.”

When we returned to Mrs. Warren’s rooms, the gloom of a London winter evening had thickened into one gray curtain, a dead monotone of colour, broken only by the sharp yellow squares of the windows and the blurred haloes of the gas-lamps. As we peered from the darkened sitting-room of the lodging-house, one more dim light glimmered high up through the obscurity.

“Someone is moving in that room,” said Holmes in a whisper, his gaunt and eager face thrust forward to the window-pane. “Yes, I can see his shadow. There he is again! He has a candle in his hand. Now he is peering across. He wants to be sure that she is on the lookout. Now he begins to flash. Take the message also, Watson, that we may check each other. A single flash - that is A, surely. Now, then. How many did you make it? Twenty. So did I. That should mean T. AT - that’s intelligible enough! Another T. Surely this is the beginning of a second word. Now, then - TENTA. Dead stop. That can’t be all, Watson? ATTENTA gives no sense. Nor is it any better as three words AT, TEN, TA, unless T. A. are a person’s initials. There it goes again! What’s that? ATTE - why, it is the same message over again. Curious, Watson, very curious! Now he is off once more! AT - why, he is repeating it for the third time. ATTENTA three times! How often will he repeat it? No, that seems to be the finish. He has withdrawn from the window. What do you make of it, Watson?”

“A cipher message, Holmes.”

My companion gave a sudden chuckle of comprehension. “And not a very obscure cipher, Watson,” said he. “Why, of course, it is Italian! The A means that it is addressed to a woman. ‘Beware! Beware! Beware!’ How’s that, Watson?”

“I believe you have hit it.”

“Not a doubt of it. It is a very urgent message, thrice repeated to make it more so. But beware of what? Wait a bit; he is coming to the window once more.”

Again we saw the dim silhouette of a crouching man and the whisk of the small flame across the window as the signals were renewed. They came more rapidly than before - so rapid that it was hard to follow them.

“PERICOLO - pericolo - eh, what’s that, Watson? ‘Danger,’ isn’t it? Yes, by Jove, it’s a danger signal. There he goes again! PERI. Halloa, what on earth- -”

The light had suddenly gone out, the glimmering square of window had disappeared, and the third floor formed a dark band round the lofty building, with its tiers of shining casements. That last warning cry had been suddenly cut short. How, and by whom? The same thought occurred on the instant to us both. Holmes sprang up from where he crouched by the window.

“This is serious, Watson,” he cried. “There is some devilry going forward! Why should such a message stop in such a way? I should put Scotland Yard in touch with this business - and yet, it is too pressing for us to leave.”

“Shall I go for the police?”

“We must define the situation a little more clearly. It may bear some more innocent interpretation. Come, Watson, let us go across ourselves and see what we can make of it.”

2

As we walked rapidly down Howe Street I glanced back at the building which we had left. There, dimly outlined at the top window, I could see the shadow of a head, a woman’s head, gazing tensely, rigidly, out into the night, waiting with breathless suspense for the renewal of that interrupted message. At the doorway of the Howe Street flats a man, muffled in a cravat and greatcoat, was leaning against the railing. He started as the hall-light fell upon our faces.