Chettle!—whom he had left only that morning in Hull, two hundred miles away, both of them agreed that the next step was still unseen, and that immediate action was yet problematical. Something had surely happened to bring Chettle up to town and to him.

"Show Mr. Chettle up here at once," he said to the waiter. "And here—bring a small decanter of whisky and a syphon of soda-water and glasses. Be sharp with 'em."

He pulled on a dressing-gown when the man had gone, and, tying its cord about his waist, went a step or two into the corridor to look out for his visitor. A few minutes elapsed; then the lift came up, and the waiter, killing two birds with one stone, appeared again, escorting the detective and carrying a tray. And Allerdyke, with a sly wink at Chettle, greeted him unconcernedly, ushered him into his room and chatted about nothing until the waiter had gone away. Then he turned on him eagerly.

"What is it?" he demanded. "Something, of course! Aught new?"

For answer Chettle thrust his hand inside his overcoat and brought out a small package, wrapped in cartridge paper, and sealed.

He began to break the seals and unwrap the covering.

"Well, it brought me up here—straight," he said. "I think I shall have to let our people at the yard know everything, Mr. Allerdyke. But I came to you first—-I only got to King's Cross half an hour ago, and I drove on to you at once. Well see what you think before I decide on anything."

"What is it!" repeated Allerdyke, gazing with interest at the package.
"You've found something of fresh importance, eh!"

Chettle took the lid off a small box and produced Lydenberg's watch and postcard on which the appointment in the High Street had been made. He sat down at the table, laying his hand on the watch.

"After you left me this morning," he said, "I started puzzling and puzzling over what had been discovered, what had been done, whether there was more that I could do. I kept thinking things over all the morning, and half the afternoon. Then it suddenly struck me—there was one thing—that I'd never done and that ought to have been done—I don't know why I'd never thought of it till then—but I'd never had this photograph out of the watch. And so I went back to the police-station and got the watch and opened it, and—look there, Mr. Allerdyke!"

He had snapped open the case of the watch as he talked, and he now detached the photograph and turning it over, laid the reverse side down on the table by the postcard.

"Look at it!" he went on. "Do you see?—there's writing on it! You see what it says? 'This is J.A. Burn this when made use of.' You see? And—it's the same handwriting as that on this card, making the appointment! Here, look at both for yourself—hold 'em closer to the light. Mr. Allerdyke—that was all written by the same hand, or I'm—no good!"

Allerdyke went close to the electric globe above his dressing-table, the photograph in one hand, the postcard in the other. He looked searchingly at both, brought them back, and laid them down again.

"No doubt of it, Chettle," he said. "No doubt of it! It doesn't need any expert to be certain sure of that. The same, identical fist, without a shadow of doubt. Well—what d'ye make of it? Here—have a drink."

He mixed a couple of drinks, pushed one glass to the detective, and took the other himself.

"Egad!" he muttered, after drinking. "Things are getting—hottish, anyway. As I say, what do you make of this? Of course, you've come to some conclusion?"

"Yes," answered Chettle, taking up his glass and silently bowing his acknowledgments. "I have! The only one I could come to. The man who sent this photograph to Lydenberg, to help him to identify your cousin at sight, is the man who afterwards lured Lydenberg into that part of Hull High Street, and shot him dead. In plain words, the master shot his man—when he'd done with him. Just as he poisoned the Frenchwoman—when he'd done with her. Mr. Allerdyke, I'm more than ever convinced that these two murders—Lydenberg's and the French maid's—were the work of one hand."

"Likely!" assented Allerdyke. "It's getting to look like it. But—whose? That's the problem, Chettle. Well, I've done a bit since I got back this afternoon. You've had something to tell me—now I've something to tell you. I've found out who it was that James gave the photograph to!"

Chettle showed his gratification by a start of pleased surprise.

"You have—already!" he exclaimed.

"Already!" replied Allerdyke. "Found it out within an hour of getting back in here. He gave it"—here, though the door was closed and bolted, and there was no fear of eavesdroppers, he sank his voice to a whisper—"he gave it to Fullaway's secretary, the woman we discussed, Mrs. Marlow. That's a fact. He gave it to her just before he set off for Russia."

Chettle screwed his lips up to whistle—instead of whistling he suddenly relaxed them to a comprehending smile.

"Aye, just so!" he said. "I was sure it lay somewhere—here. Fullaway himself, now—does he know?"

"James gave it to her in Fullaway's presence," replied Allerdyke. "She's a bit of a photographer, I understand—they were talking about photography, I gathered, one day when James was in Fullaway's office, and James pulled that out and gave it to her as a specimen of my work."

"All that came out in talk this afternoon?" asked Chettle.

"Just so. Ordinary, casual talk," assented Allerdyke.

"No suspicion roused?" suggested Chettle.

"I don't think so. Of course, you never can tell. I should say," continued Allerdyke, "that she's as deep and clever as ever they make 'em! But it was all so casual, and so natural, that I don't think she'd the slightest idea that I was trying to get at anything. However, I found this much out—she couldn't produce the photograph. Said she'd taken it home. Well—there we are! That's part one of my bit of news, Chettle. Now for part two. This woman's leading a double life. She's Mrs. Marlow as Fullaway's secretary and here at his rooms and on his business; where she lives she's Miss Slade. Eh?"

Chettle pricked his ears.

"When did you find that out?" he asked. "Since you left me this morning?"

"Found it out this afternoon," replied Allerdyke, with something of triumph. He had been strolling about the bedroom up to that moment, but now he drew a chair to the table at which Chettle sat and dropped into it close beside his visitor.

"I'll tell you all about it," he went on. "You said at Hull yesterday that you'd always found Yorkshiremen sharp and shrewd—well, this is a bit more Yorkshire work—work of my manager here in town—Mr. Appleyard. Listen!"

He gave the detective a clear and succinct account of all that Appleyard and his satellites had done, and Chettle listened with deep attention, nodding his head at the various points.

"Yes," he said, when Allerdyke had made an end, "yes, that's all right, so far. Good, useful work. The thing is—can you fully trust these two young men—your chauffeur and his brother?"

"I could and would trust my chauffeur with my last shilling," answered Allerdyke. "And as for his brother, I'll take my man's word for him. Besides, they both know—or Mr. Gaffney knows—that I'm a pretty generous paymaster. If a man does aught for me, and does it well, he profits to a nice penny!"

"A good argument," agreed Chettle. "I don't know that you could beat it, Mr. Allerdyke. Well, well—we're getting to something and to somewhere! Now, as you've told me all this, I'll just keep things quiet until I've met you and your manager to-morrow, with these two Gaffneys—we'll have a conference. I won't go near the Yard until after that. Eleven o'clock to-morrow, then, at your warehouse in Gresham Street."

He presently replaced the watch and the postcard in an inner pocket, and took his leave, and Allerdyke, letting him out, walked along the corridor with him as far as the lift. And as Allerdyke turned back to his own room, the third event of that day happened, and seemed to him to be the most surprising and important one of all.

What made Allerdyke pause as he retraced his steps along the corridor, pause to look over the balustrade to the floor immediately below his own, he never knew nor could explain. But, just as he was about to re-enter his room, he did so pause, leaning over the railings and looking down for a moment. In that moment he saw Mrs. Marlow.

A considerable portion of the floor immediately beneath him was fully exposed to the view of any one leaning over the balustrade as Allerdyke did. This was a quiet part of the hotel, a sort of wing cut away from the main building; the floor at which he was looking was given up to private suites of rooms, one of them, a larger one than the others, being Fullaway's, which filled one side of the corridor; the others were suites of two, in some cases of three rooms. As he looked over and down, Allerdyke suddenly saw a door open in one of these smaller suites—open silently and stealthily. Then he saw Mrs. Marlow look out, and she glanced right and left about her. The next instant, she emerged from the room with the same stealthiness, closed and locked the door with a key which she immediately pocketed, slipped along the corridor, and disappeared into Franklin Fullaway's suite. It was all over in less than a minute, and Allerdyke turned into his own door, smiling cynically to himself.

"She looked right and left, but she forgot to look up!" he muttered. "Ah! those small details. And what does that mean? Anyway, I know which door she came out of!"

He glanced at his watch—precisely half-past eleven. He made a note of the time in his pocket-book and went to bed. And next morning, rising early, as was his custom, he descended to the ground floor by means of the stairs instead of the lift, and as he passed the door from which he had seen Mrs. Marlow emerge he mentally registered the number. Fifty-three. Number fifty-three.

Allerdyke, who could not exist without fresh air and exercise, went for a stroll before breakfast when he was in London—he usually chose the Embankment, as being the nearest convenient open space, and thither he now repaired, thinking things over. There were many new features of this affair to think about, but the one of the previous night now occupied his thoughts to the exclusion of the others. What was this woman doing, coming—with evident secrecy—out of one set of rooms, and entering another at that late hour? He wanted to know—he must find out—and he would find out with ease,—and indirectly, from Fullaway.

Fullaway always took his breakfast at a certain table in a certain corner of the coffee-room at the hotel; there Allerdyke had sometimes joined him. He found the American there, steadily eating, when he returned from his walk, and he dropped into a chair at his side with a casual remark about the fine morning.

"Didn't set eyes on you last night at all," he went on, as he picked up his napkin. "Off somewhere, eh?"

"Spent the evening out," answered Fullaway. "Not often I do, but I did—for once in a way. Van Koon and I (you don't know Van Koon, do you?—he's a fellow countryman of mine, stopping here for the summer, and a very clever man) we dined at the Carlton, and then went to the Haymarket Theatre. I was going to ask you to join us, Allerdyke, but you were out and hadn't come in by the time we had to go."

"Thank you—no, I didn't get in until seven o'clock or so," answered
Allerdyke. "So I'd a quiet evening."

"No news, I suppose?" asked Fullaway, going vigorously forward with his breakfast. "Heard nothing from the police authorities?"

"Nothing," replied Allerdyke. "I suppose they're doing things in their own way, as usual."

"Just so," assented Fullaway. "Well, it's an odd thing to me that nobody comes forward to make some sort of a shot at that reward! Most extraordinary that the man of the Eastbourne Terrace affair should have been able to get clean away without anybody in London having seen him—or at any rate that the people who must have seen him are unable to connect him with the murder of that woman. Extraordinary!"

"It's all extraordinary," said Allerdyke. He took up a newspaper which Fullaway had thrown down and began to talk of some subject that caught his eye, until Fullaway rose, pleaded business, and went off to his rooms upstairs. When he had gone Allerdyke reconsidered matters. So Fullaway had been out the night before, had he—dining out, and at a theatre? Then, of course, it would be quite midnight before he got in. Therefore, presumably, he did not know that his secretary was about his rooms—and entering and leaving another suite close by. No—Fullaway knew nothing—that seemed certain.

The remembrance of what he had seen sent Allerdyke, as soon as he had breakfasted, to the hall of the hotel, and to the register of guests. There was no one at the register at that moment, and he turned the pages at his leisure until he came to what he wanted. And there it was—in plain black and white—

NUMBER 53. MR. JOHN VAN KOON. NEW YORK CITY, U.S.A.