By Eric Ambler

Brooke Street, in the City of London, lies off Hol -born, amid the tangle of narrow lanes between the law offices of Gray's Inn and the diamond market of Hatton Garden. Nowadays, the greater part of one side of it is taken up by the pseudo-Gothic office building of an in­surance company, but the other side is still very much as it was sixty-two years ago. There are small shops with offices about them and, at the far end, warehouses with loading platforms and wall derricks on the upper floors. It is a commercial street. At night it is silent and deserted.

The policeman who walked slowly along Brooke Street late one night in the February of 1889 must have been very bored. The fact that on the third floor of No. 24 there was a lighted window could not have interested him; he could have assumed automatically that it belonged to the office of some solicitor's clerk or bookkeeper catching up on arrears of work. It was not until well after midnight that the policeman entered history.

He was approaching the corner of Leather Lane, when he heard, coming from the darkness behind him, the sound of a door being flung open, a shout and then the quick scuffling of running feet.

He turned quickly. As he did so, he twisted the slide of his bull's-eye lantern and flashed the light in the direc­tion of the sounds.

What he saw was a man running towards him; a short, fair, hatless man with a straggling moustache and a wild look. The man dashed up breathlessly.

"Come quickly, Constable!" he gasped. "Come and see!"

The policeman was young, cautious and mindful of his training. "Now, just a moment, sir," he began; but the short man had no time for explanations.

"No, no! Come and see! I've got to show you what I've done."

The policeman tightened up inside. "Something you've done?"

"Yes, that's it!"

The policeman began to walk back along the street. The short man capered ahead of him chattering excitedly.

"You see, I've only just this minute done it. And I don't mind telling you I was scared. But I managed it, and though I dare say it's very foolish of me, I feel I've just got to show someone."

The policeman walked on grimly. He had never had a homicidal lunatic to deal with before, but this was how he had always imagined it would be.

"Of course," the lunatic was saying, "I'd like to show my wife, really, but she's not here now. And the joke is, Cousin Alfred didn't even know what I was doing." He chuckled horribly. "And now there he is, on the sheet, just as if he were alive. Here we are! It's upstairs!"

They had reached a dark doorway and the short man was standing aside for the policeman to enter. The police­man paused.

"Just a minute. Are you the owner of these premises?"

"Oh, no. I'm one of the tenants, the one who makes the smells. Friese-Greene's my name."

"I see. All right. You lead the way, Mr Greene."

"Yes, indeed. I'll go up and get everything ready for you."

The man who called himself Friese-Greene clattered away up the dark stairs.

The policeman followed soberly. He was conquering his fears now. As long as he kept behind the man nothing much could happen. The phrases of the judge who would congratulate him on his courage and steadiness began to form in his mind. By the time he had reached the third floor, he had himself well in hand.

He crossed the landing to the doorway of the room with the light in it and looked in.

He has expected an office. What he saw was a cross between a workshop and a chemical laboratory. At a bench in the centre of the room, the madman was bending over a mechanism with a light in it which he was fitting into a box. There was a disagreeable smell in the room. The policeman looked round. "Well," he said, "where is it?"

THE UNICORN