“Well, there are several possibilities. You know there are submarine companies in this country, bitter rivals. They might like to have those plans. Then, too, there are foreign governments.”

He paused. Though he said nothing, I felt that there was no doubt what he hinted at. At least one government occurred to me which would like the plans above all others.

“Once some plans of a submarine were stolen, I recall,” ruminated Kennedy. “But that theft, I am satisfied, was committed in behalf of a rival company.”

“But, Kennedy,” exclaimed Burke, “it was bad enough when the plans were stolen. Now Captain Shirley wires me that some one must have tampered with his model. It doesn’t work right. He even believes that his own life may be threatened. And there is scarcely a real clue,” he added dejectedly. “Of course we are watching all the employes who had access to the draughting-room and tracing everybody who was in the building that night. I have a complete list of them. There are three or four who will bear watching. For instance, there is a young attache of one of the embassies, named Nordheim.”

“Nordheim!” I echoed, involuntarily. I had expected an Oriental name.

“Yes, a German. I have been looking up his record, and I find that once he was connected in some way with the famous Titan Iron Works, at Kiel, Germany. We began watching him day before yesterday, but suddenly he disappeared. Then, there is a society woman in Washington, a Mrs. Bayard Brainard, who was at the Department that night. We have been trying to find her. To-day I got word that she was summering in the cottage colony across the bay from Lookout Hill. At any rate, I had to go up there to see the captain, and I thought I’d kill a whole flock of birds with one stone. The chief thought, too, that if you’d take the case with us you had best start on it up there. Next, you will no doubt want to go back to Washington with me.”

Lookout Hill was the name of the famous old estate of the Shirleys, on a point of land jutting out into Long Island Sound and with a neighbouring point enclosing a large, deep, safe harbour. On the highest ground of the estate, with a perfect view of both harbour and sound, stood a large stone house, the home of Captain Shirley, of the United States navy, retired.

Captain Shirley, a man of sixty-two or three, bronzed and wiry, met us eagerly.

“So this is Professor Kennedy; I’m glad to meet you, sir,” he welcomed, clasping Craig’s hand in both of his—a fine figure as he stood erect in the light of the portecochere. “What’s the news from Washington, Burke? Any clues?”

“I can hardly tell,” replied the secret service man, with assumed cheerfulness. “By the way, you’ll have to excuse me for a few minutes while I run back into town on a little errand. Meanwhile, Captain, will you explain to Professor Kennedy just how things are? Perhaps he’d better begin by seeing the Turtle herself.”