The chief allowed himself to take a quick searching glance at the two men he had indicated. He had already heard of Van Koon and of his sudden disappearance from the hotel after the chance encounter with Chilverton, and he now regarded him with professional interest.

"The tall man, you mean?" he asked.

"Just so," answered Allerdyke. "The other man I don't know. But that's
Van Koon. What's he here for, now? Is he in this, after all?"

The chief made no reply. He was furtively watching the two men, who had dropped into chairs at a vacant table beneath the shade of the trees and were talking to a waitress. Having taken a good look at Van Koon, he turned his attention to Van Koon's companion, a little, dapper man, smartly dressed in bright blue serge, and finished off with great care in all his appointments. He seemed to be approaching middle age; there were faint traces of grey in his pointed beard and upward-twisted moustaches; he carried his years, however, in very jaunty fashion, and his white Homburg hat, ornamented with a blue ribbon, was set at a rakish angle on the side of his close-cropped head. In his right eye he wore a gold-rimmed monocle; just then he was bringing it to bear on the waitress who stood between himself and his companion.

"You don't know the other man, either of you?" asked the chief suddenly.

Allerdyke shook his head, but Appleyard nodded.

"I know that chap by sight," he said. "I've seen him in the City—about Threadneedle Street—two or three times of late. He's always very smartly dressed—I took him for a foreigner of some sort."

The chief turned to his coffee.

"Well—never mind him," he said. "Pay no attention—so long as that man is Van Koon, I'll watch him quietly. But you may be sure he has come here on the same business that has brought us here. I—"

Allerdyke, whose sharp eyes were perpetually moving round the crowded enclosure and the little groups which mingled outside it, suddenly nudged the chief's elbow.

"Miss Slade!" he whispered. "And—Rayner!"

Appleyard had caught sight of his two fellow inmates of the Pompadour at the very moment in which Allerdyke espied them. He slightly turned away and bent his head; Allerdyke followed his example.

"You can't mistake them," he said to the chief. "I've described the man to you—a hunchback. They're crossing through the crowd towards the tea-house door."

"And they've gone in there," replied the chief in another minute. "Um!—this is getting more mysterious than ever. I wish I could get a word with some of our men who really know something! It seems to me—"

But at that moment Blindway came strolling along, his nose in the air, his eyes fixed on the roofs of the houses outside the park, and he quietly dropped a twisted scrap of paper at his superior's feet as he passed. The chief picked it up, spread it out on the marble-topped table, and read its message aloud to his companions.

"City men say the informant is here and will indicate the men to be arrested in a few minutes."

The chief tore the scrap of paper into minute shreds and dropped them on the grass.

"Things are almost at the crisis," he murmured with a smile. "It seems that we, gentlemen, are to play the part of spectators. The next thing to turn up—"

"Is Fullaway!" suddenly exclaimed Allerdyke, thrown off his guard and speaking aloud. "And, by Gad!—he's got that man Chilverton with him. This—by the Lord Harry, he's caught sight of us, too!"

Fullaway was coming quickly up the lawn from the direction of the Serpentine; he looked unusually alert, vigorous, and bustling; by his side, hurrying to keep pace with him, was the New York detective. And Fullaway's keen eyes, roving about, fell on Allerdyke and the chief and he made through the crowd in their direction, beckoning Chilverton to follow.

"Hullo—hullo!" he exclaimed, clapping a hand on Allerdyke's shoulder, nodding to the chief, and staring inquisitively at Appleyard. "So you're here, too, eh, Allerdyke? It wasn't you who sent me that mysterious message, was it?"

"What message?" growled Allerdyke. "Be careful! Don't attract attention—there are things going on here, I promise you! Drop into that chair, man—tell Chilverton to sit down. What message are you talking about?"

Fullaway, quick to grasp the situation, sat down in a chair which Appleyard pulled forward and motioned his companion to follow his example.

"I got a queer message—typewritten—on a sheet of notepaper which bore no address, about an hour ago," he said. "It told me that if I came here, to this Hyde Park tea-house, at two o'clock, I'd have this confounded mystery explained. No signature—nothing to show who or where it came from. So I set out. And just as I was stepping into a taxi to come on here, I met Chilverton, so he came along with me. What brings you, then? Similar message, eh? And what—"

"Hush!" whispered Appleyard. "Miss Slade's coming out of the tea-house!
And who's the man that's with her?"

All five men glanced covertly over their shoulders at the open door of the tea-house, some twenty to thirty yards away. Down its steps came Miss Slade, accompanied by a man whom none of them had ever seen before—a well-built, light-complexioned, fair-haired man, certainly not an Englishman, but very evidently of Teutonic extraction, who was talking volubly to his companion and making free use of his hands to point or illustrate his conversation. And when he saw this man, the chief turned quickly to Allerdyke and intercepted a look which Allerdyke was about to give him—the same thought occurred to both. Here was the man described by the hotel-keeper of Eastbourne Terrace and the shabby establishment away in the Docks!

"Miss Slade!" exclaimed Fullaway. "What on earth are you talking about?
That's my secretary, Mrs. Mar—"

"Sh!" interrupted the chief. "That's one of your surprises, Mr. Fullaway!
Quiet, now, quiet. Our job is to watch. Something'll happen in a minute."

Miss Slade and her talkative companion edged their way through the crowd and passed out to an open patch of grass whereon a few children were playing. And as they went, two or three men also separated themselves from the idlers around the tables and strolled quietly and casually in the same direction. Also, Van Koon and the man with him left their table, and, as if they had no object in life but mere aimless chatter and saunter, wandered away towards the couple who had first emerged from the enclosure. And thereupon, Fullaway, not to be repressed, burst out with another exclamation.

"My God, Chilverton!" he cried. "There is Van Koon! And, by all that's wonderful, Merrifield with him. Now what—"

The New York detective, who was under no orders, and knew no reason why he should restrain himself, wasted no time in words. Like a flash, he had leapt from his chair, threaded his way through the surrounding people, and was after his quarry. And with a muttered exclamation of anger, the chief rose and followed—and it seemed to Allerdyke that almost at the same instant a score of men, up to that moment innocently idling and lounging, rose in company.

"Damn it!" he growled, as he and Appleyard got up. "That chap's going to spoil everything. What is he after? Confound you, Fullaway!—why couldn't you keep quiet for a minute? Look there!"

Van Koon had turned and seen Chilverton. So, too, had Van Koon's companion. So, also, had Miss Slade and the man she was walking with. That man, too, saw the apparent idlers closing in upon him. For a second he, and Van Koon, and the other man stared at each other across the grass; then, as with a common instinct, each turned to flee—and at that instant Miss Slade, with a truly feminine cry, threw herself upon her companion and got an undeniably firm grip on his struggling arms.

"This is the Eastbourne Terrace man!" she panted as Allerdyke and half-a-dozen detectives relieved her. "Get the other two—Van Koon and Merrifield. Quick!"

But Van Koon was already in the secure grip of Chilverton, and the person in the light blue suit was being safely rounded up by a posse of grim-faced men.