"Ah ha, that is so, is it? I thought as much. Was it Sergius?"

"We think so," said Tuppence unblushingly.

"It would not surprise me. But you yourselves, you are under no suspicion?"

"I do not think so. We handle a good deal of bona fide business, you see," explained Tommy.

The Russian nodded.

"That is wise. All the same, I think it would be better if I did not come here again. For the moment, I am staying at the Blitz. I will take Marise-this is Marise, I suppose?"

Tuppence nodded.

"What is she known as here?"

"Oh! Miss Robinson."

"Very well, Miss Robinson, you will return with me to the Blitz and lunch with me there. We will all meet at headquarters at three o'clock. Is that clear?" He looked at Tommy.

"Perfectly clear," replied Tommy, wondering where on earth headquarters might be.

But he guessed that it was just those very headquarters that Mr. Carter was so anxious to discover.

Tuppence rose and slipped on her long black coat with its leopardskin collar. Then, demurely, she declared herself ready to accompany the Prince.

They went out together, and Tommy was left behind, a prey to conflicting emotions.

Supposing something had gone wrong with the dictaphone? Supposing the mysterious Hospital Nurse had somehow or other learnt of its installation, and had rendered it useless?

He seized the telephone and called a certain number. There was a moment's delay, and then a well known voice spoke.

"Quite O.K. Come round to the Blitz at once."

Five minutes later Tommy and Mr. Carter met in the Palm Court of the Blitz. The latter was crisp and reassuring.

"You've done excellently. The Prince and the little lady are at lunch in the Restaurant. I've got two of my men in there as waiters. Whether he suspects, or whether he doesn't-and I'm fairly sure he doesn't-we've got him on toast. There are two men posted upstairs to watch his suite, and more outside ready to follow wherever they go. Don't be worried about your wife. She'll be kept in sight the whole time. I'm not going to run any risks."

Occasionally one of the Secret Service men came to report progress. The first time it was a waiter who took their orders for cocktails, the second time it was a fashionable vacant-faced young man.

"They're coming out," said Mr. Carter. "We'll retire behind this pillar in case they sit down here, but I fancy he'll take her up to his suite. Ah! yes, I thought so."

From their post of vantage, Tommy saw the Russian and Tuppence cross the hall and enter the lift.

The minutes passed and Tommy began to fidget.

"Do you think, sir. I mean, alone in that suite-"

"One of my men's inside-behind the sofa. Don't worry, man."

A waiter crossed the hall and came up to Mr. Carter.

"Got the signal they were coming up, sir-but they haven't come. Is it all right?"

"What?" Mr. Carter spun around. "I saw them go into the lift myself. Just"-he glanced up at the clock-"four and a half minutes ago. And they haven't shown up…"

He hurried across to the lift which had just that minute come down again, and spoke to the uniformed attendant.

"You took up a gentleman with a fair beard and a young lady a few minutes ago to the second floor."

"Not the second floor. Third floor the gentleman asked for."

"Oh!" The Chief jumped in, motioning Tommy to accompany him. "Take us up to the third floor, please."

"I don't understand this," he murmured in a low voice. "But keep calm. Every exit from the Hotel is watched, and I've got a man on the third floor as well-on every floor, in fact. I was taking no chances."

The lift door opened on the third floor and they sprang out, hurrying down the corridor. Half way along it, a man dressed as a waiter came to meet them.

"It's all right, Chief. They're in No. 318."

Carter breathed a sigh of relief.

"That's all right. No other exit?"

"It's a suite, but there are only these two doors into the corridor, and to get out from any of these rooms, they'd have to pass us to get to the staircase or the lifts."

"That's all right, then. Just telephone down and find out who is supposed to be occupying this suite."

The waiter returned in a minute or two.

"Mrs. Cortlandt Van Snyder of Detroit."

Mr. Carter became very thoughtful.

"I wonder now. Is this Mrs. Van Snyder an accomplice, or is she-"

He left the sentence unfinished.

"Hear any noise from inside?" he asked abruptly.

"Not a thing. But the doors fit well. One couldn't hope to hear much."

Mr. Carter made up his mind suddenly.

"I don't like this business. We're going in. Got the master key?"

"Of course, sir."

"Call up Evans and Clydesly."

Reinforced by the other two men, they advanced towards the door of the suite. It opened noiselessly when the first man inserted his key.

They found themselves in a small hall. To the right was the open door of a bathroom, and in front of them was the sitting room. On the left was a closed door and from behind it a faint sound-rather like an asthmatic pug-could be heard. Mr. Carter pushed the door open and entered.

The room was a bedroom, with a big double bed ornately covered with a bedspread of rose and gold. On it, bound hand and foot, with her mouth secured by a gag and her eyes almost starting out of her head with pain and rage, was a middle aged fashionably dressed woman.

On a brief order from Mr. Carter, the other men had covered the whole suite. Only Tommy and his Chief had entered the bedroom. As he leant over the bed and strove to unfasten the knots, Carter's eyes went roving round the room in perplexity. Save for an immense quantity of truly American luggage, the room was empty. There was no sign of the Russian or Tuppence.

In another minute the waiter came hurrying in, and reported that the other rooms were also empty. Tommy went to the window, only to draw back and shake his head. There was no balcony-nothing but a sheer drop to the street below.

"Certain it was this room they entered?" asked Carter peremptorily.

"Sure. Besides-" The man indicated the woman on the bed.

With the aid of a pen knife, Carter parted the scarf that was half choking her, and it was at once clear that whatever her sufferings, they had not deprived Mrs. Cortlandt Van Snyder of the use of her tongue.

When she had exhausted her first indignation, Mr. Carter spoke mildly.

"Would you mind telling me exactly what happened-from the beginning?"

"I guess I'll sue the Hotel for this. It's a perfect outrage. I was just looking for my bottle of 'Killagrippe' when a man sprang on me from behind and broke a little glass bottle right under my nose, and before I could get my breath I was all in. When I came to I was lying here, all trussed up, and goodness knows what's happened to my jewels. He's gotten the lot, I guess."

"Your jewels are quite safe, I fancy," said Mr. Carter drily. He wheeled round and picked up something from the floor. "You were standing just where I am when he sprang upon you?"

"That's so," assented Mrs. Van Snyder.

It was a fragment of thin glass that Mr. Carter had picked up. He sniffed it and handed it to Tommy.

"Ethyl Chloride," he murmured. "Instant anaesthetic. But it only keeps one under for a moment or two. Surely he must still have been in the room when you came to, Mrs. Van Snyder?"

"Isn't that just what I'm telling you? Oh! it drove me half crazy to see him getting away and me not able to move or do anything at all."

"Getting away?" said Mr. Carter sharply. "Which way?"

"Through that door." She pointed to one in the opposite wall. "He had a girl with him, but she seemed kind of limp as though she'd had a dose of the same dope."

Carter looked a question at his henchman.

"Leads into the next suite, sir. But double doors-supposed to be bolted each side."

Mr. Carter examined the door carefully. Then he straightened himself up and turned towards the bed.

"Mrs. Van Snyder," he said quietly. "Do you still persist in your assertion that the man went out this way?"

"Why, certainly he did. Why shouldn't he?"

"Because the door happens to be bolted on this side," said Mr. Carter drily. He rattled the handle as he spoke.

A look of the utmost astonishment spread over Mrs. Van Snyder's face.

"Unless someone bolted the door behind him," said Mr. Carter, "he cannot have gone out that way."

He turned to Evans who had just entered the room.

"Sure they're not anywhere in this suite? Any other communicating doors?"

"No, sir, and I'm quite sure."

Carter turned his gaze this way and that about the room. He opened the big hanging wardrobe, looked under the bed, up the chimney and behind all the curtains. Finally, struck by a sudden idea, and disregarding Mrs. Van Snyder's shrill protests, he opened the large wardrobe trunk and rummaged swiftly in the interior.

Suddenly Tommy, who had been examining the communicating door, gave an exclamation.

"Come here, sir, look at this. They did go this way."

The bolt had been very cleverly filed through, so close to the socket that the join was hardly perceptible.

"The door won't open because it's locked on the other side," explained Tommy.

In another minute they were out in the corridor again and the waiter was opening the door of the adjoining suite with his pass key. This suite was untenanted. When they came to the communicating door, they saw that the same plan had been adopted. The bolt had been filed through, and the door was locked, the key having been removed. But nowhere in the suite was there any sign of Tuppence or the fair-bearded Russian, and there was no other communicating door, only the one on the corridor.

"But I'd have seen them come out," protested the waiter. "I couldn't have helped seeing them. I can take my oath they never did."

"Damn it all," cried Tommy. "They can't have vanished into thin air!"

Carter was calm again now, his keen brain working.

"Telephone down and find who had this suite last, and when."

Evans, who had come with them, leaving Clydesly on guard in the other suite, obeyed. Presently he raised his head from the telephone.