While Tom was thus watching and sleeping a somewhat different experience had fallen to the lot of Dan Frost. He had no definite plan in making a midnight visit to the vicinity of the House on the Dunes, but he hoped to discover some clue to the surrounding mysteries. From time to time during the day he had taken his field glasses to one of the upper rooms of the Inn, and scanned the countryside but nothing unusual seemed astir in the white world without. The Southern Cross had lain on the surface of the little cove all day, swaying with wind and tide, no sign of activity upon her decks. It was after ten when he started forth. The night was not quite dark, for the full moon was shining somewhere behind the thick veil of clouds. Earlier in the evening Dan had intended to go boldly to the House itself and demand an interview with old Mrs. Meath; but he reflected that he would probably be met with the excuse that Mrs. Meath was ill, and he did not know how he could force himself in, particularly past the barrier of Madame de la Fontaine's charming manner.

It was an unpleasant walk with the wind in his face, and it was nearly eleven before he turned into the long dune road, which branched from the Port Road near the Rocking Stone and led directly to the old farmhouse on Strathsey Neck. To his chagrin it appeared that all lights had been extinguished as if the inmates of the house had gone to bed.

The old farmhouse loomed before him, dark and forbidding. On either side there were outhouses, and in the rear quite near the house a barn. There was not a tree on the place; indeed, there was little vegetation upon the entire Neck, save the grass of the middle meadows which in summer furnished scant nourishment for the cattle and a flock of sheep. Now all was bleak and covered with snow, and a freshening gale swept out of the great maw of the Atlantic.

Keeping close to the fence, Frost began to make a complete circuit of the farmhouse. As he turned a corner of the south end, or rear of the house, he was relieved to see a light burning in the kitchen. He stole cautiously to a position within the shadow of the barn from which he could get a glimpse of the interior. In the kitchen standing before a deal table, he saw a young woman—not Jane, Mrs. Heath's maid-of-all-work, but a stranger,—with her hands deep in a bowl of dough. Her back was toward him, but he guessed that she was Madame de la Fontaine's maid, whom he had seen in the morning. The door into the dining-room beyond stood open, and by craning his neck, Dan could see that the room was lighter, but he could not discover whether or not it were occupied. The shutters of the dining-room were so closely barred and the curtains so tightly drawn that not a ray of light penetrated to the outside.

The girl in the kitchen proceeded busily about her work. She was evidently engaged, despite the lateness of the hour, in mixing bread.

Once while he waited patiently, to what end he hardly knew, Madame de la Fontaine entered the kitchen. She was clad in black and held in her hands what Dan took to be a ship's lamp. She stood for a moment in the doorway and spoke to the servant maid. The girl stopped her work, and taking a strip of paper, ignited it at a candle and lighted the lamp, which Madame de la Fontaine held up for her. It glowed instantly with a deep green flame, such as Tom had described as shining from a window of the House on the Dunes in the early evening.

As soon as her lamp was lighted Madame de la Fontaine left the room. Supposing that she was about to give a signal, Dan's heart leaped at the prospect of some result to his eavesdropping, and he stole carefully around to the front of the house. Presently from an upper window in the east side of the house, not the north as he had expected, he saw the green light sending forth its message across the Dunes—to whom? Probably the signal could be seen from the Inn, but it more likely was intended for the schooner in the Cove. Sure enough, as he watched, Dan saw the phenomenon of the ascending lamp on the Southern Cross, which at that identical moment Tom Pembroke was watching from his post of vantage in one of the south windows of the Inn.

A little later the signal was removed from the east window of the farmhouse and placed in a north window. Dan looked to see the answering gleam from the Inn at the Red Oak. But none came. Crouched in a corner of the fence, he waited perhaps for half-an-hour.

Suddenly a signal gleamed from the Inn, but this time it was not green as he expected, but red. In a few moments a form appeared in the window of the farmhouse, and a white hand, which he supposed was that of Madame de la Fontaine, took hold of the lamp and reversed it, so that now it showed red. The light in the Inn vanished, reappeared, vanished again. The same thing happened to the light in the House on the Dunes. And looking eastward, Dan saw the ship's red lamp perform its fantastic ascent and descent. Soon all was left in darkness. Frost slipped back to his post near the barn and looked again into the kitchen.

Madame de la Fontaine was standing in the doorway as before. The maid, turning away from the table, came at that moment to the window, and raised the sash, as though she were overheated. Presently, leaving the window open, she turned to her mistress, and Dan could hear the sharp staccato of her voice as she said something in what seemed to him her barbarous French.