The smoke was curling from the chimneys of the House on the Dunes as Dan drove up the long marsh road from the beach. He had half convinced himself that Nancy would be there, and he hoped that she herself would answer his knock. When at length the door was opened it was not by Nancy nor by Mrs. Meath, but by a stranger whom he had never seen before.

"Yes?" a pleasant voice questioned, but giving an accent to the monosyllable that made Dan think instantly of France.

He found himself facing a charming woman, her bright blue eyes looking into his with a smile that instantly attracted him. She was well-dressed, with a different air from the women he knew. And she was undeniably pretty—of that Dan was convinced, and the conviction overwhelmed him with shyness. He stood awkward and ill-at-ease; for the moment forgetting his errand. "I suppose," he stammered, "—I beg your pardon—but I suppose you are Mrs. Heath's new boarder,—Mrs. Fountain?"

"Yes," replied the strange lady with an amused smile, "that is what I imagine that I am called. My name is Madame de La Fontaine. And you—?"

"I?—Oh, yes—of course—I am Dan Frost from the Inn over yonder. I came to see Mrs. Meath to ask if my sister Nancy is here."

"Alas!" replied Madame de La Fontaine, "poor Mrs. Meath she this morning is quite unwell. She is in her room, so that I am afraid you cannot see her. But, I may tell you, there is no one else here, just myself and my servants."

"You have not seen or heard anything then of my sister, Nancy Frost?" repeated Dan.

"Nancy Frost?—your sister?—No, monsieur. I am arrived only last night and have seen no one."

"I had hoped my sister would be here. I am sorry about Mrs. Meath; perhaps I can be of some service. If you should need me at any time, I can almost always be found at the Inn at the Red Oak."

"The Inn at the Red Oak?" repeated Madame de La Fontaine, "and is that near by?"

"It is about a mile and a half by the road," Frost replied, "but you can see it plainly from the doorstep here."

The foreign lady stepped out in the crisp February air. "Can you point it out to me? I may need your assistance some time."

"You see the woods and the oak at the edge of them," said Dan, pointing across the Dunes. "That great tree is the Red Oak, the rambling old building beneath it is the Inn."

"Ah! one can see quite plainly from one house to the other, is it not so?"

"Quite," Dan replied.

"Thank you, monsieur. I trust there will be no need for assistance. But it makes one glad to know where are neighbours, especially—" she added, "while poor Mrs. Meath is ill."

As she spoke she turned to the door with the air of dismissing him, but on second thoughts she faced him again. "I wonder, Mr. Frost, will you do me a favour?"

"I shall be delighted," Dan exclaimed.

"My luggage arrived last night," said Madame de La Fontaine, "upon the ship that is at anchor in the bay. They are to bring my boxes ashore. But before that I desire to give directions to the captain at the beach, and I cannot well do so by my servant. Will you be kind enough to walk with me and show me the way?"

Dan forgot about Nancy in his eagerness to assure this unusually attractive lady that he was at her disposal. She disappeared within, and he heard her give some quick, sharp directions in French to a maid. Then in a moment she reappeared on the little porch, bonneted and wrapped for a walk in the cold.

As they set out across the Dunes, she kept up a rapid fire of questions that might have seemed inquisitive to one more accustomed to the world than Dan. He found himself in the course of that quarter of an hour talking quite freely with the charming stranger.

"No, I did not make the journey from France in the Southern Cross," she replied to one of his interrogations, "that would have been uncomfortable, I fear. But she brings over my boxes. She is arrived somewhat sooner than I was promised."

"Do you expect to signal her from the beach?"

"But yes."

"How will they know who you are?"

"Oh, they have instructions. You must think all this curious!" she commented with a smile. "You must think me an odd person."

The possible oddness of Madame de La Fontaine made less impression upon Dan than did her charm. He was conversing easily with a very lovely woman, and all else was forgotten in that agreeable sensation.

As they emerged from the Dunes upon the little beach of the Cove, Dan observed on the deck of the Southern Cross a sailor watching them through a glass. Madame de La Fontaine drew her handkerchief from beneath her cloak and waved it toward the ship.

"This is the signal," she explained, "that they were instructed to look out for. If I am not mistaken Captain Bonhomme will come to the shore for my directions. You speak French, monsieur?"

"Not at all," Dan replied.

"Ah!" sighed the lady, "you lose a great deal."

"I might have learned some this winter," said Dan; "for we have had a French gentleman as our guest at the Inn."

"Indeed! And who, may I ask, is your French gentleman?"

"His name is the Marquis de Boisdhyver. Do you, by any chance, know him?"

"The Marquis de Boisdhyver?" repeated Madame de La Fontaine. "I know the name certainly; it is an old family with us, monsieur. But I do not recall that I have ever had the pleasure of meeting any one who bore it... But see! they are lowering the boat."

They were now at the edge of the surf. Madame de La Fontaine again waved a hand in the direction of the clipper. Dan saw a small boat alongside her, into which several sailors and an officer, as it seemed, were clambering over the rail. They pushed off, and began to row vigorously for the shore.

The French lady stood watching them intently. Within a few moments the little boat was beached, the officer sprang out, advanced to Madame de La Fontaine, and saluted. She exchanged sentences with him in French of which Dan understood nothing. Then the seaman touched his cap, got into his small boat, and gave orders to push off.

"He understands no English," remarked Madame de La Fontaine. "I gave directions about my boxes. We may return now, monsieur; or doubtless I am able to find my way back alone."

"Oh no," exclaimed Dan gallantly, "I will go with you."

The lady smiled graciously. As they walked back across the Dunes, she kept up a lively conversation, no longer asking him questions, nor, he observed, giving him the opportunity to ask any.

At the door of the House on the Dunes she dismissed him finally. "I am but too grateful, Monsieur, for your kindness. I hope that we shall meet again while I dwell in your beautiful country. In the meantime, I trust you will find your sister."

Dan flushed, how could he have forgotten Nancy! Taking the hand that his new acquaintance offered, he hurried away. He met Tom on the Port Road about half a mile from the Inn and was truly worried to find that Nancy had not returned; he explained briefly his own delay in his expedition with the strange lady to the beach.

"It is certainly odd, though perhaps not so odd as stupid, that they should have anchored in the Cove just to disembark one woman's boxes. It would have been much simpler to go to the Port, as every well-bred skipper does, and had the French woman's stuff carted out. At any rate, we'll go down this afternoon and have a look at her."

By the time they reached the Inn it was noon, and still there was no word of Nancy. The dinner was a silent one, as the Marquis tactfully did not disturb his companions' preoccupation, and Mrs. Frost, who was unusually nervous, did not appear.

After the meal the two young men started for the beach. At Tom's suggestion they got a little dory from the boathouse and rowed out to the clipper. The wind had shifted to the southeast, but still there was not enough of a sea to give them any trouble; and in a few minutes they were under the bows of The Southern Cross. Dan hailed a seaman who was leaning over the gunwale and watching them with idle curiosity. If the man replied in French, it was in a variety of that tongue that Tom's limited attainments did not understand, and, annoyed by the incomprehensible replies, he asked for "le captaine". At length,—possibly attracted by the altercation at the bows,—the authoritative-looking person who had come ashore in the morning in response to Madame de La Fontaine's signal, now appeared at the gunwale and glanced below at the two young men in the dory. His expression betrayed no sign that he recognized Frost. Indeed he vouchsafed no syllable of reply to the questions Dan asked in English or to those that Tom ventured to phrase in Dr. Watson's French.

He was not, they thought, an attractive person; his countenance was swarthy, his eyes were black his hair was black, his heavy jaw was shadowed by an enormous black mustachio. A kerchief of brilliant red tied about his throat gave him the appearance of the matador in a Spanish bullfight rather than the officer of an English merchantman. He glanced at the dory occasionally, shook his head silently in response to the requests to go aboard, and at length when that did not serve to put an end to them, he shrugged his shoulders and disappeared. The seaman continued to lean over the gunwale and spat nonchalantly as though that were the measure of their appreciation of this unasked-for visit.

"I move we skip up the rope," said Tom, "and explain ourselves at close quarters."

"Thanks, no," replied Dan. "Either of those two amiable gentlemen looks capable and willing of pitching us overboard. The water is too cold for bathing."

"Very well," said Tom, "I will yield to your sober judgment for the moment; but I propose to see the inside of that ship sooner or later unless she weighs anchor in the hour and sails away. But we ought to be getting to town to make enquiries about Nancy. For Heavens' sake, Dan, where do you suppose she can be?"

They rowed back to the beach, stowed the dory in the boathouse, and set out in the sleigh for Monday Port. Diligent enquiry there, in likely and unlikely places, proved fruitless. It was nightfall when they returned to the Inn.

They were greeted by the Marquis in the bar. "Mademoiselle Nancy, she has not been found?"

"No," said Dan. "I take it from your question that she has not come home yet either."

"She is not come, no. Perhaps she stays at the House on the Dunes?"

"I do not know," Dan answered tartly. "I expect her every moment, but it is idle to conceal from you, Monsieur, that we are much concerned as to her absence."

The Marquis grew sympathetic,—optimistically sympathetic. Tom clutched at his re-assuring words, but Dan was even more irritated by the silence that Monsieur de Boisdhyver had maintained throughout the day.

Directly after supper Dan went into his mother's parlour, leaving the others to their own devices. The Marquis settled himself near the fire and was soon absorbed in reading an old folio; Tom wandered restlessly about, now up and down the long bar, now in the corridors, now on the gallery and in the court without.

The night, after the bright day, had set in raw and cold; a damp breeze blew from the southwest, and gave promise both of wind and rain. From his position under the Red Oak, Tom could see the red and green lights of The Southern Cross at her moorings in the Cove below, and across the Neck the lighted windows of the House on the Dunes. Over all else the night had cast its black damp mantle.

As he stood watching, deeply anxious for the welfare of the girl he loved, he noticed a new light appear in one of the upper windows of the House on the Dunes—not yellow as is the light of candles, but green like the light on the port side of the clipper in the Cove. Had he not seen the lights from the other windows he could have thought it was another ship on the ocean side of the Neck.

He looked for a long time at the tiny spark in the distance, wondering what whim had induced Mrs. Meath to shade her candles with so deep a green. As he strolled back toward the Inn, he glanced through the windows of the bar where the Marquis still read by the fireside. Suddenly the old gentleman, as Tom curiously watched him, laid his book down on the table and rose from his chair. He looked about the room and then advanced to the window. Tom instinctively slipped behind the trunk of the great oak. Monsieur de Boisdhyver stood for several moments peering into the darkness. Then he turned away and crossed the room to the door into the front hall. It flashed through Tom's mind that possibly the Marquis had started on another of his mysterious tours. He ran down again into the court far enough from the house to command a view of the entire facade, and watched curiously, particularly the north wing. All was dark, save for the lights below.

Suddenly he saw the flicker of a candle in one of the windows, not of the north wing, but of the south. A moment's glance, and he made sure that it was the room occupied as a sleeping apartment by Monsieur de Boisdhyver.

The Marquis was standing by the window, with his face pressed close to the pane, peering out into the night. He still held the candle in his hand. To Dan's surprise, he placed it carefully on the broad window-sill, and drew down the dark shade to within a foot of the sill, blotting out all save a narrow band of light. Then the Marquis disappeared for several moments into the interior of the room. Dan was about to turn back into the house, when again Monsieur de Boisdhyver came to the window. He did not raise the shade, but inserted between the windowpane and the candle a strip of dark green paper. It was translucent and had the effect of sending a beam of green light southward, across the meadows and the dunes, to meet—Tom suddenly realized—the rays of the green light from the House on the Dunes.

Was it a signal being exchanged, and between whom? The coincidence of green lights from the Inn and the House on the Dunes, at the same moment, was too marked to be without significance. To what end was the Marquis de Boisdhyver exchanging mysterious signals with some one in that lonely farmhouse, and what did they mean?

Tom repressed his agitation and remained for some time watching the two green lights that glowed toward one another over the dark landscape.

Suddenly the light in the House on the Dunes was extinguished; then, momentarily it shone again, but quickly went out and left the great sweep of dunes in darkness. Two minutes later the same thing took place in the window of the south chamber of the Inn. The light flashed and was gone, flashed again and shone no more.

Tom went in, by a rear entrance, to the bar. The Marquis was seated by a table, absorbed in reading. He started as Tom entered. "Still no word of Mademoiselle?" he piped.

"Still no word, monsieur," Pembroke answered laconically. He also seated himself in the candle light and took up the last issue of the Port News.

"Do you know what has become of Dan?" Pembroke asked presently.

"Monsieur Frost he has been closeted with madame his mother for the past half-hour. You have no further plans for seeking Mademoiselle? For myself, I grow alarmed."

"I know nothing but what you know, monsieur. Nancy has not returned. There has been no word of her. We shall have to wait." With tremendous effort to conceal his agitation and annoyance, Tom resumed his reading.

Monsieur de Boisdhyver glanced at him for a moment with a little air of interrogation, then shrugged his shoulders slightly and turned again to his French paper.