"You girls are doing better with every minute!" was his lively praise one morning as they rowed the "Water Witch" toward the houseboat. Their practice was over for the day, and Lieutenant Jimmy was to take luncheon with them.

It had been a particularly interesting morning. Madge felt more drawn toward the young lieutenant than on any previous occasion. He had been telling her and Phyllis of his life in the Navy, his hopes and aspirations, and Phyllis had purposely drawn him into describing his invention. He had just completed a model of his torpedo-boat destroyer and expected to take it to Washington within a few days. He was to show his model boat to a committee of naval experts, who were to decide whether his invention were of value.

Aside from the pleasure it gave him to tell the girls of his invention he had another graver reason for doing so. He had decided to ask Phyllis to do him a great favor. From the beginning of their acquaintance the young man had been impressed with Phil's sterling qualities. She was loyal to her friends and absolutely dependable. He felt certain that she would respect a confidence and keep a secret. He believed her to be the one person he could trust absolutely. Yet he did not wish to draw her into a promise without the knowledge of at least one of her friends. For this reason he had chosen to make Madge his confidante also.

Just how to begin he hardly knew, and it was not until they had rowed within close range of the houseboat, where Tom Curtis and Alfred Thornton stood waving from the deck, that he said nervously:

"Won't you and Miss Morton stop rowing for a moment, Miss Alden? I wouldn't have bored you with the story of my invention, except that I wish to ask you a strange favor. If I go away in a few days, of course my work-shop will be closely watched and guarded. Yet I shall not feel it to be perfectly safe. I alone know that I am being spied upon, that certain men are shadowing me ready to report every movement that I make. If, after leaving here, I should fall ill unexpectedly, or—disappear suddenly, the secret of my invention might never be known. So I wish to ask you, Miss Alden, to keep a small, square box, which I shall give you before I leave. I shall ask you not to examine its contents unless some unusual circumstance should develop, when you feel obliged to ascertain what the box contains. You may think it strange that I do not ask one of my men friends to do this favor for me. But I have a special reason for desiring to place the box in the care of some one who will never be suspected of having it. Will you keep it for me, say for a week, or until I ask you or write to you for it?"

The skiff had nearly reached the houseboat. Madge and Phyllis were allowing the "Water Witch" to drift in. Their friends on board had seen them and were signaling for them to come aboard.

Madge's usually sunny face was clouded with disapproval. Why should Lieutenant Lawton wish a young girl like Phyllis, a mere acquaintance, to guard a mysterious box for him? What could possibly happen to him when he went to Washington! It was all too vague and too absurd. She decided that she and Phyllis would have nothing to do with Lieutenant Lawton's invention.

"I don't believe, Phil, that you and I ought to do what Lieutenant Lawton asks unless he takes us fully into his confidence," she protested.

Phyllis closed her lips with an expression of quiet resolution. "I will take care of the box for you while you are away, Lieutenant Lawton," she declared. "If Madge doesn't wish to have anything to do with it, she will keep your secret, at any rate. I know it will be all right, Madge; I am sure you will agree with me," she ended coaxingly, turning to her chum. "We could not refuse to do such a simple favor for a friend. And I think Lieutenant Lawton is a true patriot to give his invention to his country, instead of selling it to make a fortune, as so many other men would do, and I am proud to aid him in even the smallest way."

Lieutenant Lawton blushed. It occurred to Madge that she and Phyllis knew little of the young officer's real character. Suppose, after all, he did not intend to present his discovery to his Government? Were she and Phil to be used as dupes? A long, searching look into the young man's earnest face seemed to reassure her.