SHE waited till he disappeared in the shadow of the garden; then pulled up the ladder and placed it in a drawer within the wardrobe, from whence she had extracted it, and closed the windows.

He had left very definite instructions, and she went over them in her mind to make absolutely sure.

The medallion she knew. She had prepared a drawing especially for this man whose influence was the guiding and dominant thing in her life.

She looked round carefully to remove all trace of the visitor's presence. Then she unlocked the door and went out.

As she passed the little museum, Sir Ralph and his guest emerged. He looked at her in some surprise.

"Hello, Vera," he said pleasantly, for him, "I thought you were with the others."

"I've been doing my accounts," she said, with a little grimace.

Sir Ralph chuckled. In his more pleasant moods he took a humorous view of his own economies.

He was fastening the door of the museum, when Vera intervened.

"I'd like to see those medallions of yours again," she said.

Sir Ralph was pleased. Vera took too little interest in his collection to satisfy him. It was one of his grievances that she did not enter into what he termed the "larger side of his life."

"Come along, come along," he said, "only do not provoke Hilary to a discussion on art, because he is the veriest Philistine."

He chuckled again.

The museum was the one room in the house lighted by electricity. Here once more Sir Ralph had been guilty of an extravagance which was entirely foreign to his nature. He had had a storage battery installed especially for the illumination of his treasure house.

The girl looked at the medallions with more than usual interest. She had seen them before, and recently, though this Sir Ralph did not know. She had a twofold object in asking for this inspection. Her husband had grown nervous as a result of the activity of the "Red Hand," and had signified his intention of changing all the locks. She wanted to make certain that he had not carried out his plans.

Her first glance reassured her. They had not been altered, nor had he changed the position of the medallions.

"They are very beautiful," she said.

In point of fact she thought them very uninteresting, but it was not politic to express this view.

"They grow on you, do they not?" said Sir Ralph, enthusiastically. "I shall make a connoisseur of you in time, Vera."

She went downstairs ahead of the two men, in a thoughtful mood.

It was after midnight when the little party broke up, and retired to their rooms.

Frank was one of the last to go upstairs. He passed through the drawing-room, and found Vera tidying away the chessmen with which Sir Ralph and Hilary had been amusing themselves.

He would have gone straight on, but something induced him to stop.

"Good night, Lady Morte-Mannery," he said.

She was bending over the table and did not trouble to raise her head.

"Good night, Mr. Gallinford," she said.

He still waited.

"I feel that I ought to explain something that is in my mind," he said, a trifle uncomfortably. He had no great command of language, and was somewhat embarrassed.

"I shouldn't, if I were you," she said, quietly. "Let matters go as they are, and be charitable."

She was in a melting mood to-night. For no reason that she could think of, she felt a desire to stand well with the world, and especially with that section of the world which this good-looking English youth represented.

"There is a key-word," she said, "which explains the most contradictory situations — the most unlikely and unthinkable follies. You may know that key-word."

"I only know one," he said, gently, "and that is 'Love.'"

Vera smiled at him. It was a dazzling, human smile, that revealed in a flash the deeps of her nature.

"That is the word," she said, and went on with her tidying.

He stood a second longer; then, with another "Good night" he left her, puzzled and a little ashamed of his own attitude towards her.

At the head of the stairs Marjorie was waiting to say "Goodnight," and in a moment all thought of the woman he had left in the drawing-room below, and her cryptic utterances, were obliterated from his mind.

*      *      *      *      *

Vera had been reading before her bedroom fire. She had spent the whole of the night reading and thinking. The reading had been mechanical; she could not recall a single sentence or one situation from the thrilling novel which lay upon her knee.

She looked up at the little clock over the mantelpiece. The hands pointed to a quarter to four.

She rose and took from a hanging cupboard a long dark rain-coat, and this she put on over her dressing-gown, buttoning it carefully so that it should not inconvenience her movements.

She unlocked and opened a drawer of her writing-table and took out a red morocco case.

This she again unlocked with a key attached to a bunch she had taken from under her pillow. The case was apparently empty, but she pressed a spring and the bottom of the box flew up.

Three beautifully fashioned keys lay on the velvet in the false bottom. She took them in her hand, closed the box, and extinguished the light.

She waited by the door for a moment or two, listening. Then she opened it and stepped out into the dark corridor.

She had twenty or thirty yards to walk, but her mocassined feet made no sound upon the thick carpet. The house lay wrapped in slumber, as silent as death.

She could hear nothing save the rattle within the wainscot of a foraging mouse. She walked on until she came to the museum. Here she halted again, listening.

Sir Ralph slept in a room on the farther side and, fortunately, was a heavy sleeper. Hilary had the room on the other.

She inserted the key, opened the rosewood door, took the other key and turned it in the steel door.

Noiselessly the well-oiled lock shot back. She pushed the door open and entered, closing both doors behind her. She could not lock them from the inside, but there was no chance of a casual passer observing that it had been opened — even if casual wanderers were likely at this hour of the morning.

She took from the pocket of her rain-coat a tiny electric lamp, and flashed it over the cases. She found the one she wanted, unshuttered it deftly, opened the glass case, and lifted out the medallion.

She made a quick inspection of it, to make sure that she had the right jewel.

Noiselessly she slipped through the door, locked it behind her, and fastened the outer covering quickly.

Then she turned to retrace her steps to her room.

She took one step and then stopped, rooted to the ground with terror and dismay, for, confronting her, she saw a bulky form.

There was not enough light to show her his face, but she knew it was Hilary George.

"Who's there?" he asked, softly.

She was paralysed with terror. She could not force her tongue to speak.

"Who is that?" he asked, and his voice rose.

With a superhuman effort she recovered her self-possession.

If he spoke louder he would wake Sir Ralph, and that would be the end of things.

"It is I," she said, speaking in the same tone.

"Lady Morte-Mannery? I am sorry," he whispered. "I thought I heard somebody in the grounds, and I listened, but heard nothing more, so I got a little uneasy.

"It's all right," she said, speaking in the same tone as before. "I have been to Sir Ralph's room to get a little veronal. I cannot sleep."

With a whispered apology he went back to his room.

It was on the other side of the treasure house, and she wondered if she had made any noise. Had he seen her come out? His next words lifted a weight from her heart.

"I couldn't see where you came from," he said, "or who you were. I hope I didn't frighten you?"

"Oh, no," she said, lightly.

With another apology he went into his room, and closed the door softly behind him.

She flew along the passage to her room, her heart beating wildly. Once in the room, she locked the door and drew the curtain across it. Then she lit the gas with an unsteady hand. She caught a glimpse of her face in the mirror over the fireplace, and was shocked at its drawn and haggard appearance.

There was still part of the work to be done.

Hilary had heard somebody in the garden. That would be Festini. She looked to make sure that she had the jewel, then she turned out the light again, opened the shutters, and crept out on to the balcony.

She saw a dark figure standing in the shadow of some bushes. The man came forward as she appeared.

"Catch!" she whispered.

He held out his hand as she threw.

He caught the medallion neatly, and put it in his pocket, then turned without a word and plunged into the bushes.

She stood for a moment — a little disappointed feeling in her heart. After all she had risked, all she had dared, she had hoped for some word of thanks.

She was turning to re-enter the room when a sibilant voice held her.

Her heart bounded. He had come back. She looked down at the dark figure beneath. "Did you get it?" he whispered, in a low tone.

"Get it?" she said, in bewilderment, "I have just given it to you."

"Given it to me?" his voice was harsh. "You have given me nothing. I have been waiting here for half an hour."

She staggered back against the balustrade, half sick with fear.

"Tell me, tell me," said the voice impatiently, growing louder. "Who was it you gave it to?"

"I gave it to a man," she said, faintly.

"Which way did he go?"

"Through those bushes," she said. Without another word he ran in the direction the other man had taken.

She had time to get back to the room, close the shutters and pull the curtains, before she fell half-swooning upon the ground.

Festini was light of foot, quick, and with the almost cat-like ability of picking his way in the dark. He had not gone twenty yards before he saw the man ahead.

There was no time for finesse.

Fortunately for him, Festini had changed his plans. He had dropped the idea of coming by cycle, and his car now stood, purring gently, in a little lane which adjoined the house.

As he sighted the man ahead, he whipped out his automatic pistol and fired twice.

Without a sound the man sank to the ground.

Festini had no time to examine his victim. He knew that he was still alive, as he bent over him and searched his waistcoat pockets.

In one of these he had hoped to find the jewel, but it was not there.

But it was in the clasped hand of the stricken man.

Festini found it, wrenched open the fingers, and possessed himself of the prize.

"Now! Do your worst," he hissed, as he swung round and shook his fist, as at a world that was at war with him, "do your worst!"

The sound of the shot had awakened the people of the house. Lights appeared in two or three rooms.

Vera, lying on the floor, was roused to consciousness by a loud knocking at her door.

She got up slowly. Her head was still dizzy, and she staggered as she walked.

"Who is there?" she asked.

"It is I," said her husband's voice. "Open the door. Are you hurt?"

She plunged her hands into a jug of water that stood on the washstand, and passed them over her face. The touch of the chilly water revived her. She dabbed her face with a towel with one hand as she opened the door with the other.

"What is it?" she asked.

She was steadying herself. She had heard the shot, and she was prepared for the worst.

Sir Ralph was in his dressing-gown.

"Where was the firing?" he asked.

"I heard no firing," she said, steadily.

"Somebody fired a pistol in the garden," said Sir Ralph.

She heard Hilary's voice in the passage.

"Are you all right, Lady Morte-Mannery?" said his voice.

"I am quite all right," she replied. "What is wrong?"

Her voice was shaky and high-pitched, but in a dull way she knew that her agitation would be excusable. There had been shots in the garden, somebody had been shot — who? At that moment there came to her a quick pang of fear.

"Somebody is shot?" she asked, tensely. "Who is shot?"

"There was a man in the garden, trying to enter the house," said Hilary's voice. "Possibly he was detected."

Sir Ralph crossed the room, and, opening the shutters, went out on to the balcony. Two men were already on the lawn below.

"Have you found anything?" he called. He was addressing the two hastily-aroused servants who were conducting the search outside.

Vera listened; her heart almost stopped beating, when the groom's voice replied —

"There's a man shot in the shrubbery, Sir Ralph. He looks like a foreigner."

She clenched her hands and waited — rigid  — expressionless.

"What sort of man?" asked Sir Ralph, testily. "What do you mean by a foreigner, Philip?"

"Well, he's a clean-shaven gentleman," said the servant. "I don't think he's badly hurt. A tall man."

A great joy surged over the woman.

It was not he; whoever it was, whether this wounded man lived or died — it was not Festini.

She listened. There was a new voice.

"It's all right, Sir Ralph," it said.

She recognized it, and set her teeth. Part of the conversation came to her in little gusts.

"It was just a little clip of a bullet across the temple... that is the second time they have missed me.... I'm afraid you've lost something...."

It was the voice of Tillizini.

In the big hall they assembled, a dishevelled assembly, hastily garmented.

Tillizini's wound was a superficial one. The bullet had struck behind his ear, glancing over the parietal bone and temporarily stunning him. He was very cheerful.

"I only came down to-night by car," he said, "because I received information which led me to believe that the attempt would be made upon you. Now," he said, "I am ready."

He stood up.

"I want to examine your little museum," he said, "and discover what is lost."

"Oh, I couldn't have lost anything from there," said Sir Ralph, confidently. "There are alarms in every window, and almost every pane."

"There are no alarms on the door, are there?" asked Tillizini.

Sir Ralph looked surprised.

"They are not necessary," he said.

He led the way, and the others followed.

He opened the treasure house, and they flocked in behind him. He was a little in advance of Tillizini, and he turned in the doorway to switch on the light.

At that moment Vera saw the evidence of her criminal folly. On the top of one of the shuttered cases was the little jewelled electric lamp which Sir Ralph had in a fit of unusual generosity given her.

Tillizini saw it too. He was as quick as she, and quicker to move. With one step he stood between the tell-tale lamp and the gaze of the half-awake people in the doorway. His hand went out and covered it.

When Sir Ralph turned the lamp had disappeared.

There was a quick inspection.

"It's gone!" cried the knight. "They have taken the Leonardo!"

"I thought they had," said Tillizini calmly, "and I thought I should be able to restore it — but, for the moment, that pleasure is denied me."

"But is it possible?" said Sir Ralph, bewildered. "Nobody could have got in here without my knowing!"

He was almost tearful in his grief.

"It was invaluable," he said. "It cannot be replaced. It is the only one of the kind in the world. What does it mean — what does it mean, Tillizini? You must tell me everything! I insist upon knowing! I won't be kept in the dark!"

He raved and stormed as though Tillizini had been responsible for the theft. It was some time before he became calmer, and then the Italian was by no means informative.

Vera, silent and watchful, waited. Whatever happened, Festini was safe! By now he would be far on his way to London. He had the parcel, that was enough: she had served him, she asked for no more.

From the moment that Tillizini had put out his hand and covered the lamp she knew that he had guessed her secret. Would he betray her? To her surprise and relief he made no reference to what he must have seen and known.

Yet he was distressed and worried — she saw that — but it was with the greater issue, with the danger which confronted civilization.

He walked up and down the hall — a remarkable figure, with the white bandage encircling his head, his hands thrust deep into his pockets, his chin blue and unshaven, his eyes tired, with an infinite weariness.

He took no part in the fruitless discussion as to how the thief effected an entry. He had all the information he required on that subject. He paused in his walk and took from his pocket a shining object — laid it in the palm of his hand and examined it.

Sir Ralph, attracted by the glow of dull gold in his hand, stepped forward with a startled cry.

"Why, that is the locket!" he cried.

Tillizini shook his head.

"It is one very much like it," he said, "but it is not the one. It is the famous locket that was stolen from the Dublin collection, and which is at the present moment supposed to be at the bottom of the North Sea. It was given to a fellow-passenger on that boat to guard and to return to me. You remember I was charged with the investigation of its disappearance?"

He walked to the fireplace.

There were two overhanging gas-brackets which gave a clear light.

He held the medallion with both hands, using only two fingers of each. He gave it a sharp twist and it fell in two.

Sir Ralph uttered an exclamation.

"Why, I did not know that these things opened!" he said wonderingly.

"I could most devoutly wish that they did not," said Tillizini grimly.

He damped his finger a little, and drew forth from the locket's interior what looked like four discs of paper, as indeed they were. They were covered with fine writing — so fine that it was almost impossible to read them without the aid of a reading glass.

"Do you understand Italian?" asked Tillizini.

"A little," said Sir Ralph, "but not enough to read this."

"Take a good look at it," said the other; "it is from the hand of the greatest genius that ever lived since Jerusalem was a vassal state of Rome."

He spoke reverently — almost adoringly — of his famous compatriot.

"That is the hand of Leonardo da Vinci," he said in a hushed voice.

"And what is it all about?" asked Frank, "and isn't it written backwards?"

He had been examining the microscopic writing with his keen eyes.

Tillizini smiled.

"The master wrote with his left hand invariably — always working back to the left. This will help you."

He drew from his pocket a tiny mirror in a leather case.

"Read," said Tillizini.

Frank carried the little discs nearer to the light, and brought them with the mirror closer to his eyes. Marjorie, watching him, saw his lips move as he read the Italian, saw his brows pucker in a puzzled frown, then her lover looked up suddenly.

"Why," he said, "this is all about a plague." Tillizini nodded.

"The Great Plague," he said, "or, as modern scientists call it, the Fourth Plague, which broke out simultaneously in Italy and Ireland in the same year. It was the one plague which our modern doctors are unable to understand or fathom. As a matter of fact, the only man who understood it was Leonardo da Vinci. He was, as you know well, Sir Ralph, more than a painter. He had the scientific mind perfectly developed. He was the first to foresee the coming of the aeroplane and the armoured ship. He was an engineer, a sculptor, a chemist, and — "

He spread out his hands.

"What is the use? I cannot enumerate his qualities," he said. "He was so above the heads of his contemporaries that they were unable to realize what kind of genius was in their midst. Even posterity can hardly do him justice. He alone understood the Fourth Plague — its meaning and its cause.

"That plague came into existence by the cultivation of a germ, though this, of course, he did not know because the microscope was denied him, but he guessed it — with that wonderful, God-like intuition of his, he guessed it," said Tillizini, his face glowing with enthusiasm and pride.

"The conditions under which the plague came into being, conditions which were undreamed of, even by those who saw them under their eyes, were revealed to Leonardo da Vinci. Ordinarily," he went on, "they would in this year of grace be produced."

"What do you mean by that?" asked Sir Ralph.

"Under the modern system," said Tillizini, "that plague could never appear again. But there are six drugs which you might find in the British Pharmacopoeia," he continued, "which, if you were to mix them, would produce a gas."

He spoke impressively, and with the assurance of the practical scientist.

"That gas, passed through a filter of vegetable matter, would set up conditions which made the plague of 1500 possible."

"Good God!" said Frank. "Do you mean to say that you can produce a plague synthetically?"

Tillizini nodded.

"That is exactly what Leonardo da Vinci discovered. This is the secret."

He held the flimsy discs in his hands.

"There is no doubt that Leonardo did produce a plague synthetically, two years after. At any rate, some such outbreak occurred in the town where his laboratory was situated. It is believed that, as a result of that plague, Mona Lisa Gioconda lost her life."

"Oh, that is the woman in the picture," said Marjorie.

"That is the woman in the picture," repeated Tillizini, "the one woman in the world whom Leonardo ever loved. The one great softening influence that ever came into his life. His investigations into the cause of the plague he set forth, concisely, on these little filaments. The lockets he fashioned himself. One, as you know — "

"I know the history," said Sir Ralph. "I was telling Mr. Gallinford only the other day. How extraordinary it is that that old-world story should be revived."

"But why do the 'Red Hand' want these lockets?"

"They only want one. Either one will do," said Tillizini. "Don't you realize? To-morrow, with the aid of a man with even the most elementary knowledge of chemistry, they could devastate London — and not only London, but the whole of England, or, if it please them, the whole of Europe, working from different centres."

As the little party stood stricken to silence, the full horror of the danger dawning upon them, Tillizini heard a long-drawn sigh.

Vera had stumbled forward in a dead faint, and Frank had just time to catch her before she fell.