“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-shell 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 Saturday,” he said, “was the 27th, the day that Parrish died ...”