If there were committed in London the crime of the century--a crime so tremendous that the names of the chief actors in this grisly drama were on the lips of every man, woman and talkative child in Europe--you might walk into a certain department of Scotland Yard with the assurance that you would not meet within the confining walls of that bureau any police officer who was interested in the slightest, or who, indeed, had even heard of the occurrence save by accident. This department is known as the Parley Voos or P.V. Department, and concerns itself only in suspicious events beyond the territorial waters of Great Britain and Ireland. Its body is on the Thames Embankment, but its soul is at the Central Office, or at the Surete or even at the Yamen of the police minister of Pekin.

It is sublimely ignorant of the masters of crime who dwell beneath the shadows of the Yard, but it could tell you, without stopping to look up reference, not only the names of the known gunmen of New York, but the composition of almost every secret society in China.

A Pole had a quarrel with a Jew in the streets of Cracow, and they quarrelled over the only matter which is worthy of quarrel in that part of Poland. The sum in dispute was the comparatively paltry one of 260 Kronen, but when the Jew was taken in a dying condition to the hospital he made a statement which was so curious that the Chief of Police in Cracow sent it on to Vienna and Vienna sent it to Berne and Berne scratched its chin thoughtfully and sent it forward to Paris, where it was distributed to Rio de Janeiro, New York, and London.

The Assistant Chief of the P.V. Department came out of his room and drifted aimlessly into the uncomfortable bureau of Mr. McNorton.

"There's a curious yarn through from Cracow," he said, "which might interest your friend Beale."

"What is it?" asked McNorton, who invariably found the stories of the P.V. Department fascinating but profitless.

"A man was murdered," said the P.V. man lightly, as though that were the least important feature of the story, "but before he pegged out he made a will or an assignment of his property to his son, in the course of which he said that none of his stocks--he was a corn factor--were to be sold under one thousand Kronen a bushel. That's about L30."

"Corn at L30 a bushel?" said McNorton. "Was he delirious?"

"Not at all," said the other. "He was a very well-known man in Cracow, one Zibowski, who during the late war was principal buying agent for the German Government. The Chief of the Police at Cracow apparently asked him if he wasn't suffering from illusions, and the man then made a statement that the German Government had an option on all the grain in Galicia, Hungary and the Ukraine at a lower price. Zibowski held out for better terms. It is believed that he was working with a member of the German Government who made a fortune in the war out of army contracts. In fact, he as good as let this out just before he died, when he spoke in his delirium of a wonderful invention which was being worked on behalf of the German Government, an invention called the Green Rust."

McNorton whistled.

"Is that all?" he said.

"That's all," said the P.V. man. "I seem to remember that Beale had made one or two mysterious references to the Rust. Where is he now?"

"He left town last night," replied McNorton.

"Can you get in touch with him?"

The other shook his head.

"I suppose you are sending on a copy of this communication to the Cabinet," he said--"it may be rather serious. Whatever the scheme is, it is being worked in London, and van Heerden is the chief operator."

He took down his hat and went out in search of Kitson, whom he found in the lobby of the hotel. James Kitson came toward him eagerly.

"Have you news of Beale?"

"He was at Kingston this morning," said McNorton, "with Parson Homo, but he had left. I was on the 'phone to the inspector at Kingston, who did not know very much and could give me no very definite news as to whether Beale had made his discovery. He interviewed the tramp early this morning, but apparently extracted very little that was helpful. As a matter of fact, I came to you to ask if he had got in touch with you."

Kitson shook his head.

"I want to see him about his Green Rust scare--Beale has gone single-handed into this matter," said the superintendent, shaking his head, "and he has played the lone game a little too long."

"Is it very serious?"

"It may be an international matter," replied McNorton gravely, "all that we know at present is this. A big plot is on foot to tamper with the food supplies of the world and the chief plotter is van Heerden. Beale knows more about the matter than any of us, but he only gives us occasional glimpses of the real situation. I have been digging out van Heerden's record without, however, finding anything very incriminating. Up to a point he seems to have been a model citizen, though his associates were not always of the best. He has been seen in the company of at least three people with a bad history. Milsom, a doctor, convicted of murder in the 'nineties; Bridgers, an American chemist with two convictions for illicit trading in drugs; Gregory--who seems to be his factotum and general assistant, convicted in Manchester for saccharine smuggling; and a girl called Glaum, who is an alien, charged during the war for failing to register."

"But against van Heerden?"

"Nothing. He has travelled a great deal in America and on the Continent. He was in Spain a few years ago and was suspected of being associated with the German Embassy. His association with the Millinborn murder you know."

"Yes, I know that," said James Kitson bitterly.

"Beale will have to tell us all he knows," McNorton went on, "and probably we can tell him something he doesn't know; namely, that van Heerden conducts a pretty expensive correspondence by cable with all parts of the world. Something has happened in Cracow which gives a value to all Beale's suspicions."

Briefly he related the gist of the story which had reached him that morning.

"It is incredible," said Kitson when the chief had finished. "It would be humanly impossible for the world to buy at that price. And there is no reason for it. It happens that I am interested in a milling corporation and I know that the world's crops are good--in fact, the harvest will be well above the average. I should say that the Cracow Jew was talking in delirium."

But McNorton smiled indulgently.

"I hope you're right," he said. "I hope the whole thing is a mare's nest and for once in my life I trust that the police clues are as wrong as hell. But, anyway, van Heerden is cabling mighty freely--and I want Beale!"

But Beale was unreachable. A visit to his apartment produced no results. The "foreign gentleman" who on the previous day had called on van Heerden had been seen there that morning, but he, too, had vanished, and none of McNorton's watchers had been able to pick him up.

McNorton shifted the direction of his search and dropped into the palatial establishment of Punsonby's. He strolled past the grill-hidden desk which had once held Oliva Cresswell, and saw out of the tail of his eye a stranger in her place and by her side the darkly taciturn Hilda Glaum.

Mr. White, that pompous man, greeted him strangely. As the police chief came into the private office Mr. White half-rose, turned deadly pale and became of a sudden bereft of speech. McNorton recognized the symptoms from long acquaintance with the characteristics of detected criminals, and wondered how deeply this pompous man was committed to whatever scheme was hatching.

"Ah--ah--Mr. McNorton!" stammered White, shaking like a leaf, "won't you sit down, please? To what--to what," he swallowed twice before he could get the words out, "to what am I indebted?"

"Just called in to look you up," said McNorton genially. "Have you been losing any more--registered letters lately?"

Mr. White subsided again into his chair.

"Yes, yes--no, I mean," he said, "no--ah--thank you. It was kind of you to call, inspector----"

"Superintendent," corrected the other good-humouredly.

"A thousand pardons, superintendent," said Mr. White hastily, "no, sir, nothing so unfortunate."

He shot a look half-fearful, half-resentful at the police officer.

"And how is your friend Doctor van Heerden?"

Mr. White twisted uncomfortably in his chair. Again his look of nervousness and apprehension.

"Mr.--ah--van Heerden is not a friend of mine," he said, "a business acquaintance," he sighed heavily, "just a business acquaintance."

The White he had known was not the White of to-day. The man looked older, his face was more ............