“Yes, I suppose so. What about Tassel?”

“Tassel’? My dear Linckes, if you’re going to shadow him I shall begin to regret I ever put you on to the case. Why, you might just as well suspect Caryu!”

“Ah!” said Linckes, and saw the chief’s lips twitch.

The telephone-bell rang sharply before Masters had time to speak again. He unhooked the receiver.

“Hallo! What? Sir Charles? Yes, put him through to me at once, will you?” He nodded at Linckes. "I thought Winthrop would ring up. I told him about you. Our White Hope. Yes? Hallo! Is that Sir Charles? Good-morning! Yes, he’s here now. Yes, I’ve told him all I know. No, I don’t think so. Well, he hasn’t had much chance to yet. What? Yes, certainly! Now? All right, Sir Charles, I’ll send him along. What? Oh, I see! Yes, all right. Good-bye!”

He put the receiver back.

“Sir Charles wants you to go along to his house now, Linckes—16, Arlington Street. Get along there as quickly as you can, will you? I want you to put every ounce of your brain into this. It’s a big chance for you, you know.”

Linckes rose, and drew a deep breath.

II.

HALF an hour later he stood in the library of No. 16, Arlington Street, taking in his surroundings with appreciative eyes. He was examining a fine old chest by the window when Winthrop came in.

Linckes turned. He beheld a tall, slim man of perhaps thirty-five years old, with an open, handsome face, in which sparkled a pair of dark eyes, singularly expressive, and fringed by long black lashes. Winthrop held Linckes’ card in his hand, and he came forward, smiling. The smile dispersed the slight sternness about his mouth, and left it boyish and charming. Very simply he told Linckes all that he knew, while the young detective listened intently, occasionally putting a question.

“And that’s all,” Winthrop ended ruefully. “’Tisn’t much to go on, is it?

“No; very little. You don’t suspect anyone yourself?”

“I don’t. I admit it looked like the work of an outsider, but I just don’t see how it can be. Masters first suspected Ruthven, my secretary; but that’s impossible. I can account for all his movements, and I know that he didn’t go near Caryu’s place during the three days that the plans were there, for the simple reason that he was with me at Millbank.”

“There might be an accomplice.”

Winthrop screwed up his nose, perplexed.

“Well, of course there might be. But, considering that Ruthven himself doesn’t know the key to the safe, I don’t see how that helps. Besides, Caryu has a most elaborate alarm thing in his safe-room. Only he and I know the workings to it. Either of us could enter the room without disturbing it, provided we did not try to get in at the window, or any funny trick like that, but no one else could. Whoever did it must have watched the place for months; might even have been in the household. Probably was, because there were no signs of burglary. We had no idea anything had been tampered with until we had ample proof that Russia had learnt the secret of those new subs. I tell you it’s absolutely incomprehensible!”