other side, he swam away lustily toward the stern, and climbed upon the deck again, where he seated himself under the shade of the awning.

But Nick Carter had not permitted himself to sink beneath the water merely for the purpose of disappearing in order to reappear again at another spot. In fact, his request for the bathing-suit, and for the opportunity to use it, had been with a well-defined motive other than the mere pleasure to be derived from a dip in the sea.

The detective really wished to examine the bottom of the cove. The idea did not occur to him because he believed that he would discover any suggestive trace of the pirate down there, but he put the thought into words because it was his professional habit never to neglect even the most trivial and apparently unimportant item from his investigations.

The idea of examining the bottom of the Sound for traces of a vessel which had passed over that spot would be absurdly ludicrous; but, all the same, there was one idea which had been suggested to Nick by the description[52] Kane had given him of the pirate craft, and he believed it to be more than possible that there might be an indication of the fact—if it were a fact—to be found at the bottom, not far from the buoy to which the yacht was moored.

[52]

It will be remembered that he asked Kane if he thought the pirate craft was a submarine, and it must be recorded that, notwithstanding the reply he received, he thought it more than probable that the silent approach of the vessel had been accomplished in that way.

Nick knew that the bottom of that cove was soft, and largely composed of clay, especially at points where it attained as great a depth as that where the yacht was moored.

Clay is impressionable. It will receive and hold the shape of an article which rests upon it a considerable time, and the detective argued that if the Shadow, as she was called, had at any moment rested upon the bottom at that particular point, she would have left her mark there. That she was a submarine, or at least was capable of diving beneath the surface and remaining there for some time, he had not a doubt. The very fact that she had approached the Goalong so silently that her proximity was not suspected was sufficiently satisfactory of that idea to him.

The water was, fortunately, unusually clear, and Nick had no difficulty in examining the bottom almost at his leisure. When he came 

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