From a drawer in the table he produced a board on which he pinned down the letter with a drawing-pin at each corner. Then he dipped a paint-brush into one of the bottles and carefully painted the whole surface of the sheet with some invisible fluid. “So!” he said, “we’ll leave that to dry and see if we can find out any little secrets, eh? That little tray’ll do the trick if there’s any monkey business to this letter of yours, Miss Trevert. That’ll do the trick, eh, what?” He paced the room as he talked, not waiting for an answer, but running on as though he were soliloquizing. Presently he turned and swooped down on the board. “Nothing,” he ejaculated. “Now for the acids!” With a little piece of sponge he carefully wiped the surface of the letter and painted it again with a substance from another bottle. “Just hold that to the fire, would you, Euan?” he said, and gave MacTavish the board. He resumed his pacing, but this time he hummed in the most unmelodious voice imaginable: She was bright as a butterfly, as fair as a queen, Was pretty little Polly Perkins, of Paddington Green. “It’s dry!” MacTavish’s voice broke in upon the pacing and the discordant song. “Well?” Dulkinghorn snapped out the question. “No result!” said Euan. He handed him the board. Dulkinghorn cast a glance at it, swiftly removed the letter, held it for an instant up to the electric light, fingered the paper for a moment, and handed the letter back to Mary. “If it’s code,” he said, “it’s a conventional code and that always beats the expert ... at first. Go to Rotterdam and call on my friend, Mr. William Schulz. I’ll give you a letter for him and he’ll place himself entirely at your disposition. Euan will take you over. Holland is on your beat, ain’t it, Euan? When do you go next?” “To-morrow,” said the King’s Messenger. “The boat train leaves Liverpool Street at ten o’clock.” “You’ll want a passport,” said Dulkinghorn, turning to the girl. “You’ve got it there? Good. Leave it with me. You shall have it back properly viséed by nine o’clock to-morrow morning. Where are you stayin’? Almond’s Hotel. Good. I’ll send the letter for Mr. William Schulz with it!” “But,” Euan interjected mildly, after making several ineffectual efforts to stem the torrent of speech, “do you really think that Miss Trevert will be well advised to risk this trip to Holland alone? Hadn’t the police better take the matter in hand?” “Police be damned!” replied Dulkinghorn heartily. “Miss Trevert will be better than a dozen heavy-handed, heavy-footed plain-clothes men. When you get to Rotterdam, Miss Trevert, you trot along and call on William Schulz. He’ll see you through.” Then, to indicate without any possibility of misunderstanding, that his work had been interrupted long enough, Dulkinghorn got up, and, opening the sitting-room door, led the way into the hall. As he stood with his hand on the latch of the front door, Mary Trevert asked him: “Is this Mr. Schulz an Englishman?”