Granet, a few days later, brought his car to a standstill in front of an ordinary five-barred gate upon which was painted in white letters "Market Burnham Hall." A slight grey mist was falling and the country inland was almost blotted from sight. On the other side of the gate a sandy driver disappeared into an avenue of ragged and stunted elm trees, which effectually concealed any view of the house.

"Seems as though the girl were right," Granet muttered to himself. "However, here goes."

He backed his car close to the side of the hedge, and laying his hand upon the latch of the gate, prepared to swing it open. Almost immediately a figure stepped out from the shrubs.

"Halt!"

Granet looked with surprise at the khaki-clad figure.

"Your name and destination?" the man demanded.

"Captain Granet of the Royal Fusiliers, home from the Front on leave," Granet replied. "I was going up to the Hall to call on Miss Worth."

"Stay where you are, if you please, sir," the man replied.

He stepped back into the sentry box and spoke through a telephone. In a moment or two he reappeared.

"Pass on, please, sir," he said.

Granet walked slowly up the avenue, his hands behind him, a frown upon his forehead. Perhaps, after all, things were not to be so easy for him. On either side he could see the stretches of sand, and here and there the long creeks of salt water. As he came nearer to the house, the smell of the sea grew stronger, the tops of the trees were more bowed than ever, sand was blown everywhere across the hopeless flower-beds. The house itself, suddenly revealed, was a grim weather-beaten structure, built on the very edge of a queer, barrow-like tongue of land which ended with the house itself. The sea was breaking on the few yards of beach sheer below the windows. To his right was a walled garden, some lawns and greenhouses; to the left, stables, a garage, and two or three labourer's cottages. At the front door another soldier was stationed doing sentry duty. He stood on one side, however, and allowed Granet to ring the bell.

"Officers quartered here?" Granet inquired.

"Only one, sir," the man replied.

The door was opened almost immediately by a woman-servant. She did not wait for Granet to announce himself but motioned him to follow her into a large, circular, stone hall, across which she led him quickly and threw open the door of the drawing-room. Isabel Worth was standing just inside the room, as though listening. She held out her hand and there was no doubt about her welcome.

"Captain Granet," she said almost in a whisper, "of course you'll think we are all mad, but would you mind coming upstairs into my little sitting-room?"

"Of course not," Granet acquiesced. "I'll come anywhere, with pleasure. What a view you have from here!"

He glanced through the high windows at the other end of the room. She laid her fingers upon his arm and led him towards the door.

"Quietly, please," she whispered. "Try and imagine that you are in a house of conspirators."

She led him up the quaint stone staircase, spiral-shaped, to the first floor. Arrived there, she paused to listen for a moment, then breathed a little more freely and led him to a small sitting-room at the end of a long passage. It was a pleasant little apartment and looked sheer out over the sea. She threw herself down upon a sofa with a sigh of relief, and pointed to a chair.

"Do sit down, Captain Granet," she begged. "I am really not in the least insane but father is. You know, I got back on Wednesday night and was met at once with stern orders that no visitors of any sort were to be received, that the tradespeople were to be interviewed at the front gates--in fact that the house was to be in a state of siege."

Granet appeared puzzled.

"But why?"

"Simply because dad has gone out of his senses," she replied wearily. "Look here."

She led him cautiously to the window and pointed downwards. About fifty yards out at sea was a queer wooden structure, set up on strong supports. From where they were, nothing was to be seen but a windowless wall of framework and a rope ladder. Underneath, a boat was tethered to one of the supports. About thirty yards away, a man was rowing leisurely around in another small boat.

"That's where father spends about twelve hours a day," she said. "What he is doing no one knows. He won't even allow me to speak of it. When we meet at meals, I am not supposed to allude to the fact that he has been out in that crazy place. If ever he happens to speak of it, he calls it his workshop."

"But he is not alone there?" Granet asked.

"Oh, no! There are two or three men from London, and an American, working with him. Then do you see the corner of the garden there?"

She pointed to a long barn or boathouse almost upon the beach. Before the door two sentries were standing. Even from where they sat they could hear the faint whirr of a dynamo.

"There are twenty men at work in there," she said. "They all sleep in the barn or the potting sheds. They are not allowed even to go down to the village. Now, perhaps, you can begin to understand, Captain Granet, what it is like to be here."

"Well, it all sounds very interesting," he remarked, "but I should think it must be deadly for you. Your father invents no end of wonderful things, doesn't he?"

"If he does, he never speaks about it," the girl answered a little bitterly. "All that he wants from me is my absence or my silence. When I came back the other night, he was furious. If he'd thought about it, I'm sure he'd have had me stay in London. Now that I am here, though, I am simply a prisoner."

Granet resumed his seat and lit the cigarette which she insisted upon his smoking.

"Well," he observed, "it does seem hard upon you, Miss Worth. On the other hand, it really is rather interesting, isn't it, to think that your father is such a man of mysteries?"

The girl sighed.

"I suppose so," she admitted, "but then, you see, father is almost brutal about taking any one into his confidence. He never tells even me a thing, or encourages me to ask a question. I think for that reason I have grown rather to resent his work and the ridiculous restriction he places upon my freedom because of it."

A parlourmaid entered with tea, a few minutes later, and Granet moved to his hostess' side upon the sofa. He showed no more interest in outside happenings. He was an adept at light conversation and he made himself thoroughly agreeable for the next hour. Then he rose quickly to his feet.

"I must go," he declared.

She sighed.

"It has been so nice to have you here," she said, "but if you only knew how difficult it was to arrange, it, you'd understand why I hesitate to ask you to come again."

"Why shouldn't you come and lunch with me to-morrow at the Golf Club?" he asked.

She hesitated. It was obvious that the suggestion appealed to her.

"I believe I could," she assented. "Captain Chalmers has a small motor-car he'd lend me, and if I go out with my golf clubs it would be all right. Very likely father will sleep out there and we sha'n't see anything of him until to-morrow."

Granet stepped once more to the window. The mists had rolled up more thickly than ever and the queer little structure was almost invisible. A bright light, however, fell upon the water a little distance away.

"Your father has electric light out there," he remarked.

"Yes, they have a wire from the shed," she told him. "Whatever he's trying to do, he needs a very intense and concentrated light at times."

Granet drew a little sigh.

"Well, I hope it's something that'll do us a bit of good," he said. "We need it. The Germans are miles ahead of us with regard to all new-fangled ideas."

She opened her lips and closed them again. Granet, who had suddenly stiffened into rigid attention, felt a quick impulse of disappointment.

"I have rung the bell for my own maid," she said. "She will show you out of the place. Don't let any one see you, if you can help it."

"And to-morrow?" he asked. "You will lunch with me?"

"I will be at the Golf Club," she promised, "at one o'clock."

Granet was conducted almost stealthily down the stairs and into the avenue. Half-way to the gate he paused to listen. He was hidden from sight now by the gathering twilight and the rolling mists. From behind the house came the softly muffled roar of the tide sweeping in, and, with sharper insistence, the whirr of machinery from the boathouse. Granet lit a cigarette and walked thoughtfully away. Just as he climbed into the car, a peculiar light through the trees startled him. He stood up and watched. From the top of the house a slowly revolving searchlight played upon the waters.