Israels jerked a thumb upwards. "Next landing. Door on left," he e.j.a.c.u.l.a.t.ed nervously.

The superintendent pushed by the man. He knew that the critical moment had come. With his quick judgment of men he had summed up Mr. Israels.

Whatever the Jew's morals, it was evident that he had a wholesome respect for his own oily skin. He would not risk himself to save the neck of another man. Foyle's intentions were simple. He would steal quietly up the second flight of stairs, burst the door open if it were locked, and seize the man he was in search of in his sleep. But his plans were frustrated.

He had not taken two steps when a woman peeped from an adjoining room.

He caught one glimpse of her in the semi-darkness with a police whistle at her lips. He sprang forward, and as he did so a shrill, ear-piercing blast rang out. Green was close behind him.

She shrieked as the detective tore the whistle from her, and he felt her slender figure entwine itself about him. Down he went, with his companion on top of him, and another woman's loud hysterical cries added to the pandemonium. Foyle picked himself up and, lifting the girl bodily, flung her without ceremony into the room from which she had emerged. From above a voice shouted something, and a knife whizzed downwards and struck quivering in the bare boards of the landing, grazing Green's shoulders.

All need for caution was gone now. Foyle had dropped his jemmy and his hand closed over his pistol. Only as a last resource would he use it, but if he had to--well, there could be no harm in having it handy. A door slammed as the two detectives climbed the second flight of stairs.

Green flung himself against the one that had been indicated by Israels, and the flimsy fastening gave way under the shock of his thirteen stone.

There was no one in the room. Savagely Heldon Foyle turned and caught the handle of a second door. It turned, and they entered the room, empty like the first, but with an open window looking out on a series of low roofs a dozen feet below. And over the roofs a shadowy figure of a man was clambering hurriedly. He could only dimly be seen.

Green clambered through on to the window-sill and dropped. He was unlucky. A projecting piece of wood caught his foot, and he staggered and lost time. Before he had recovered himself the fugitive was out of sight, and the sound of his progress had ceased. Foyle called to him to come back and, without waiting to see whether his orders were obeyed, made his way back again to the first-floor landing. Israels was still there, very white and shaky, as the superintendent struck a match.

"Where's that girl?" said the detective curtly. "The one who gave the alarm."

"My daughter? She thought you were burglars. She didn't know."

"Where is she?"

Without waiting for a reply he entered the room whence she had emerged and, striking another match, applied it to a gas-bracket. A fat woman was sitting up in bed looking at him timorously. He paid no heed to her, but stooped to look under the bed. When he straightened himself Green had rejoined him.

"The girl gave us away," exclaimed Foyle. "Here, you, where is she gone?" He shook the woman roughly by the shoulder. "Go to the bottom of the stairs, Green, and see that no one slips in or out. Take that chap outside down with you."

"My daughter?" exclaimed the woman helplessly. "She has gone to stay with her aunt. We are respectable people. You frightened her. We don't like the police coming here."

"Highly respectable," repeated Foyle under his breath. Aloud he said menacingly, "We shall soon know whether you are respectable. Where does the girl's aunt live?"

"Twenty-two Shadwell Lane," was the reply, glib and prompt.

Foyle looked for an instant penetratingly at her. Her eyes dropped. His hand went to his pocket and he calmly lighted a cigar. Then he went downstairs to where Green was on guard and politely apologised to Israels. Casually he repeated the question he had put to the woman. Yes, the Jew had seen his daughter go out. She said she was going to her aunt. Her aunt lived at 48 Suss.e.x Street.

"I see," said the superintendent quietly. "The fact is, of course, that she is not your daughter, and that she has not gone to her aunt's. You are in an awkward corner, my man," he went on, changing his tone and moving a step nearer. "Better tell us the truth. Your wife has let me know something."

As if mechanically, he was dangling a pair of shiny steel handcuffs in his fingers. Handcuffs seldom formed a part of his equipment, but to-night he had carried them with him on the off-chance that he might have to use them. The Jew shrank away, but the sight had proved effective.

"I'll tell all the truth," he whined, with an outspreading gesture of his hands. "I've done no wrong. You can't hurt me. She came here a day or two ago and paid five pounds for a week's lodging. I was to tell any one who inquired that she was my daughter. She slept with my wife. What harm was there? I am poor. Five pounds isn't picked up like that every day. The man came afterwards. He said he was a journalist and asked me to buy him a typewriting machine. I asked no questions. Why should I?"

His manner was that of a much-injured man. Foyle cut him short now and again as he rambled on with a question. In half an hour he felt that he had extracted a fair amount of truth, mingled though it was with cunning lies. He guessed now that the woman whom he had vaguely seen was she whose part in the mystery of the house in Grosvenor Gardens had always been shadowy and vague. She could be none other than Lola Rachael, little Lola of Vienna, otherwise the Princess Petrovska.

CHAPTER XVII

There was nothing more to be done at Grave Street. Heldon Foyle remained in the house while Green walked to the chief divisional station, and in an hour or two the divisional inspector with a couple of men arrived.

Then Foyle saw to a strict search of the house from top to bottom.

Nothing there was that seemed to possess any great importance as bearing on the case. The man who had fled over the roof had used a single room, apparently as bed- and sitting-room, so it was to this place that the detectives devoted chief attention.

"He must have been sleeping in his clothes," grumbled Green. "He hadn't time to dress. There's the typewriter the note was written on."

He sat down before a rickety table and, inserting a piece of paper in the machine, slowly tapped out the alphabet, and after a brief inspection pa.s.sed the paper on to the superintendent, who scanned it casually, and was about to throw it away when something gripped his attention.

"This looks queer," he muttered, and held the paper up slantingly away from the gas-jet in order to examine it by what photographers call transmitted light.

His brows were drawn together tightly. The sheet of paper which Green had used was an ordinary piece of writing-paper. On its rough surface Foyle had noted a slight sheen, unusual enough to attract his attention. Even he would not have noticed it but for the angle in which he had happened first to look at it when he took it from Green. It might be an accidental fault in the manufacture of the paper. Yet, trivial as it seemed, it was unusual, and one of the chief a.s.sets in detective work is not to let the unusual go unexplained.

"It's the same typewriter. There can be no question of that," said Green. "You can see that the 'b' is knocked about and the 'o' is out of line."

"That's all right," said Foyle. "I wasn't thinking of that. It looks to me as if there's some sympathetic writing on this."

He held the paper so that the heat from the gas-jet warmed it. Every moment he expected that the heat would bring something to light on the paper. He gave a petulant exclamation as nothing happened, and his eyes roved over the table whence Green had taken the paper. He believed that he was not mistaken, that there was something written which could be brought to light if he knew how. He knew that there were chemicals that could be used for secret communications which could only be revealed by the use of other chemicals--a process something akin to development in photography. It was unlikely, if the user of the room had used some chemical agent, that he would have thought of destroying and concealing it. But there was nothing on the table that suggested itself to Foyle as having been used in the connection. Keenly he scrutinised the room, his well-manicured hand caressing his chin.

"Ah!" he exclaimed at last. He had noted a small bottle of gum arabic standing on the cast-iron mantelpiece.

Now, gum arabic can be used for a variety of purposes, and it has the merit of invisible ink of being made decipherable by quite a simple process which minimises the risk of accidental disclosure. The superintendent held the paper to the gas again for a few minutes. Then from a corner of the room he collected a handful of dust--no difficult process, for it was long since the place had felt the purifying influence of a broom--and rubbed it hard on the rough surface of the paper. A jumble of letters stood out greyly on the surface. He looked at them hard, and Green, peeping over his shoulder, frowned.

"Cipher!" he exclaimed.

It was undoubtedly cipher, but whether a simple or abstruse one Foyle was in no position to judge. He had an elementary knowledge of the subject, but he had no intention of attempting to solve it by himself.

There were always experts to whom appeal could be made. A successful detective, like a successful journalist, is a man who knows the value of specialists--who knows where to go for the information he wants. That meaningless jumble of letters could only be juggled into sense by an expert. Foyle nevertheless scrutinised them closely, more as a matter of habit than of reading anything from them. They were--

UJQW. BJNT. FJ. UJM. FJTV. UIYIQL. SK. DQUQZOKKEYJPK. ANUJ. M.Q.

NG. N. AYUQNQIX. IGZ. ANUJ. SIO. IGZ. SMPPN. RT. 12845 HGZVFSF.

"We'll let Jones have a go at that," he said. "Anything else now?"

Some one handed him the knife that had been thrown at him on the landing and a curious leather sheath that had been picked up near the bed. From the bottom of the sheath depended a leather ta.s.sel. Foyle looked it over and failed to discover any manufacturer's name. He slipped the weapon into his pocket with the mental reflection that it looked Greek. The search went on from attic to cellar, and profuse notes were taken of everything found, with its exact position. The elaborate trouble taken by these men to describe minutely in writing every little thing would have seemed absurd to any one not versed in the ways of the Criminal Investigation Department. Yet nothing was done that was not necessary.

An error of an inch in a measurement might make all the difference when the case came on for trial.

Foyle and Green left the house in charge of the divisional man. Already a description had been circulated of the man they had failed to surprise; but as neither had caught more than a glimpse of a shadowy figure in the darkness, they had had to rely on the descriptions given by Israels and his wife. And even if that estimable pair had really tried honestly to give a fair description of the man--which the detectives thought was extremely doubtful--there could be little hope that it was accurate. If the average man tries to describe the appearance of his most intimate friend and then asks a stranger to identify him, he will realise how misleading such descriptions may be even at the best of times. Yet the Criminal Investigation Department had to work with such material as they had.

Heldon Foyle was very silent as they trudged side by side out of Whitechapel into the silent City streets--for there are no taxicabs to be found in the East End at such hours. The case was developing; but though he was beginning to have a hazy glimpse into some of its workings, there was much that remained a mystery to him. His questionings of Israels had satisfied him that the man who had escaped was neither Grell nor Ivan. He could not blame himself for not effecting an arrest. Looking back over the night's events, he could not see that he could have taken further precaution. If he had taken more men the escape would have occurred just the same over the roofs, for he would still have felt it his duty to question Israels. He could not have foreseen that the ready-witted Lola was there, nor that she should have so ingeniously given the alarm. The luck had been against him.

Nevertheless he had gained an important fact. Lola was in London and was obviously acting in concert with Grell. It was easier to look for two persons than one. Sooner or later he would lay hands on them and solve the mystery of the murder. He clenched his fists resolutely as his thoughts carried him away. Meanwhile there was the cipher. If that could be de-coded it might be valuable.

Green's voice broke in upon his thoughts.

"We didn't find anything bearing on Waverley."

"Waverley?" repeated Foyle. "Oh yes, I had almost forgotten him."

For an hour after they had reached Scotland Yard the superintendent laboured at his desk, collecting reports and writing fresh chapters in the book which held all the facts in relation to the crime, so far as he knew them. He slipped the result of his labours at last in an envelope and left them over to be dealt with by the inspector in charge of the Registry, which is a department that serves as official memory to Scotland Yard.

"That is all right," he said, and stretched himself.