Herr Schulz listened attentively and without interruption until Robin had reached the end of his story.

"There's one thing you haven't explained," he said, "and that's how Miss Trevert came to walk into the hands of these precious ruffians ..."

"There, perhaps, I can help you," said the doctor from behind one of Herr Schulz's rank cigars; "I have it from Miss Trevert herself. Some one impersonating you Mr.--er, ahem,--Schulz--telephoned her this morning, after she had left her letter of introduction here, asking her to come out to lunch at your country-house. She suspected nothing and went off in the car they sent for her ..."

"By George!" said the big man thoughtfully; "I suspected some game of this kind when I heard of the attempt to get at that letter of introduction. If I only could have got hold of Marbran this morning ..."

"Marbran!" said Robin thoughtfully. "When I read Dulkinghorn's letter just now I thought I had heard that name before. Of course--Victor Marbran! That was it! I remember now! He knew Hartley Parrish in the old days. Parrish once said that Marbran would do him an injury if he could.

Who is Marbran, sir?"

All unconsciously he paid the tribute of 'sir' to Herr Schulz's undoubted habit of command.

"Victor Marbran," replied the big man, "is Elias van der Spyck & Co., a firm which made millions in the war by trading with the enemy. In every neutral country there were, of course, firms which specialized in importing contraband for the use of the Germans, but van der Spyck & Co.

brought the evasion of the blockade to a fine art. They covered up their tracks, however, with such consummate art that we could never bring anything home to them. In fact, it was only after the armistice that we began to learn something of the immense scope of their operations. There was a master brain behind them. But it was never discovered. It strikes me, however, that we are on the right track at last ..."

"By Jove ...!" exclaimed Robin impressively. "Hartley Parrish!..."

The big man raised a hand.

"_Attentions!_" he interposed suavely. "The chain is not yet complete. I wonder what this van der Spyck letter of Miss Trevert's contained that made Victor Marbran and the secretary chap so desperately anxious to get hold of it. For you understand, don't you?" he said briskly, turning to Robin, "that they were after that and that alone. And they risked penal servitude in this country to get it ..."

Robin nodded.

"To save their necks in another," he said.

"I have the letter here," mildly remarked the doctor from his corner of the room. "Miss Trevert gave it to me!"

He produced a white envelope and drew from it a folded square of slatey-blue paper. In great excitement Robin sprang forward.

"You're a downy bird, Doctor, I must say," he remarked, "fancy keeping it up your sleeve all this time!"

He eagerly took the letter, spread it out on the table, and read it through whilst Herr Schulz looked over his shoulder.

"Code, eh?" commented the big man, shaking his head humorously. "If it beats Dulkinghorn, it beats me!"

From his note-case Robin now drew a folded square of paper identical in colour with the letter spread out before them.

"I found this on the carpet beside Parrish's body," he said. "Look, it's exactly the same paper ..."

Behind the tortoise-sh.e.l.l spectacles the big man's eyes narrowed down to pin-points as he caught sight of the sheet which Robin unfolded and its series of slits.

"Aha!" he cried--and his voice rang out clear through the room--"the grill, eh? Well, well, to think of that!"

He took the slotted sheet of paper from Robin's hands and laid it over the letter so that it exactly covered it, edge to edge and corner to corner. In this way the greater part of the typewriting in the letter was covered over, and only the words appearing in the slots could be read. And thus it was that Robin Greve, Herr Schulz, and Dr.

Collingwood, leaning shoulder to shoulder, read the message that came to Hartley Parrish in the library at Harkings....

ELIAS VAN DER SPYCK & CO.

GENERAL IMPORTERS

ROTTERDAM Rotterdam 25th Nov.

_Codes_ A.B.C.

Liebler's

_Personal_

Dear Mr. Parrish,

Your favour of even date to hand and contents noted. _The last_ delivery of steel was to time but we have had _warning_ from the railway authorities that labour troubles at the docks are likely to delay future consignments. _If you don't_ mind we should prefer to _settle_ the question of future delivery _by Nov. 27_ as we have a board meeting on the 30th inst. While we fully appreciate your own difficulties with labour at home, _you_ will understand that this is a question which we cannot afford to adjourn _sine_ _die._

Yours faithfully,

pro ELIAS VAN DER SPYCK & CO.

"'The last ... warning,'" Robin read out, "'if you don't ... settle ...

by Nov. 27 ... you ... die ...!'"

He looked up. "Last Sat.u.r.day," he said, "was the 27th, the day that Parrish died ..."

"The grill," remarked the big man authoritatively, "is one of the oldest dodges known to the Secret Service. It renders a conventional code absolutely undecipherable as long as it is skilfully worded, as it is in this case. You send your conventional code by one route, your key by another. I make no doubt that this was the way in which van der Spyck & Co. transacted their business with Hartley Parrish. They simply posted their conventional code letters through the post in the ordinary way, confident that there was nothing in them to catch the eye of the Censor's Department. The key might be sent in half a dozen different ways, by hand, concealed in a newspaper, in a parcel ..."

"So this," said Robin, pointing at the letter, "was what caused Hartley Parrish to make his will. It would lead one to suppose that it was what induced him to commit suicide were not the presumption so strong that he was murdered. But who killed him? Was it Jeekes or Marbran?"

Herr Schulz pitched his cigar-stump into an ash-tray.

"That," he said, "is the question which I am going to ask you gentlemen to help me answer. You will realize that legally we have not a leg to stand on. We are in a foreign country where, without first getting a warrant from London, we can take no steps whatever to run these fellows in. To get the Dutch police to move against these gentry in the matter of the a.s.sault upon Miss Trevert would waste valuable time. And we have to move quickly--before these two lads can get away. I therefore propose that we start this instant for the Villa Bergendal and try, if we are not too late, to force Marbran or Jeekes or both of them to a confession. That done, we can hold them if possible until we can get the Dutch police to apprehend them at the instance of Miss Trevert. Then we can communicate with the English police. It's all quite illegal, of course! You have a car, I think, Mr. Greve! You will come with us, Dr.

Collingwood? Good! Then let us start at once!"

Robin intervened with a proposal that they should call _en route_ at his hotel to see if there were any telegrams for him.

"Manderton knows I am in Rotterdam," he explained, "and he promised to wire me the latest developments in the enquiry he is conducting."

"Miss Trevert should be fully recovered by this," put in the doctor; "apart from a little sickness she is really none the worse for her disagreeable experience. If there was anything you wanted to ask her ..."

"There is," said Robin promptly. "Her reply to one question," he explained, turning to Herr Schulz, "will give us the certainty that Parrish was murdered and did not commit suicide. It will not delay us more than five minutes to stop at her hotel in pa.s.sing, We will then call in at my place. We should be at the Villa within half an hour from now ..."

"Gentlemen," said Herr Schulz as they prepared to go, "I know my Mr.

Victor Marbran. You should all be armed."

Robin produced the pistol he had taken from Jeekes. Herr Schulz slipped a Browning pistol into the breast-pocket of his jacket and, producing a long-barrelled service revolver, gave it to the doctor.

"There are three of them, I gather, counting the chauffeur," commented the big man, pulling on his overcoat, "so we shall be equally matched."

Darkness had fallen upon Rotterdam and the lights from the houses made yellow streaks in the water of the ca.n.a.l as the car, piloted by Robin, drove the party to Mary Trevert's hotel.

They found the girl, pale and anxious, in the lounge.