Tarling gave one glance before he turned to the girl, who was endeavouring to push past him, and catching her by the arm gently thrust her back into the passage.

"What is wrong? What is wrong?" she asked in a terrified whisper. "Oh, let me go to mother."

She struggled to escape from his grip, but he held her firmly.

"You must be brave, for your own sake — for everybody's sake," he entreated her.

Still holding her arm, he forced her to the door of the second inner room. His hand felt for the electric switch and found it.

He was in what appeared to be a spare bedroom, plainly furnished, and from this a door led, apparently into the main building.

"Where does that door lead?" he asked, but she did not appear to hear him.

"Mother, mother!" she was moaning, "what has happened to my mother?"

"Where does that door lead?" he asked again, and for answer she slipped her trembling hand into her pocket and produced a key.

He opened the door and found himself in a rectangular gallery overlooking the hall.

She slipped past him, but he caught her and pushed her back.

"I tell you, you must be calm, Odette," he said firmly, "you must not give way. Everything depends upon your courage. Where are the servants?"

Then, unexpectedly, she broke away from him and raced back through the door into the wing they had left. He followed in swift pursuit.

"For God's sake, Odette, don't, don't," he cried, as she flung herself against the door and burst into her mother's room.

One glance she gave, then she fell on the floor by the side of her dead mother, and flinging her arms about the form kissed the cold lips.

Tarling pulled her gently away, and half-carried, half-supported her back to the gallery. A dishevelled man in shirt and trousers whom Tarling thought might be the butler was hurrying along the corridor.

"Arouse any women who are in the house," said Tarling in a low voice. "Mrs. Rider has been murdered."

"Murdered, sir!" said the startled man. "You don't mean that?"

"Quick," said Tarling sharply, "Miss Rider has fainted again."

They carried her into the drawing-room and laid her on the couch, and Tarling did not leave her until he had seen her in the hands of two women servants.

He went back with the butler to the room where the body lay. He turned on all the lights and made a careful scrutiny of the room. The window leading on to the glass-covered balcony where he had been concealed a few hours before, was latched, locked and bolted.

The curtains, which had been drawn, presumably by Milburgh when he came for the wallet, were undisturbed. From the position in which the dead woman lay and the calm on her face he thought death must have come instantly and unexpectedly. Probably the murderer stole behind her whilst she was standing at the foot of the sofa which he had partly seen through the window. It was likely that, to beguile the time of waiting for her daughter's return, she had taken a book from a little cabinet immediately behind the door, and support for this theory came in the shape of a book which had evidently fallen out of her hand between the position in which she was found and the book-case.

Together the two men lifted the body on to the sofa.

"You had better go down into the town and inform the police," said Tarling. "Is there a telephone here?"

"Yes, sir," replied the butler.

"Good, that will save you a journey," said the detective.

He notified the local police officials and then got on to Scotland Yard and sent a messenger to arouse Whiteside. The faint pallor of dawn was in the sky when he looked out of the window, but the pale light merely served to emphasise the pitch darkness of the world.

He examined the knife, which had the appearance of being a very ordinary butcher's knife. There were some faint initials burnt upon the hilt, but these had been so worn by constant handling that there was only the faintest trace of what they had originally been. He could see an "M" and two other letters that looked like "C" and "A."

"M.C.A.?"

He puzzled his brain to interpret the initials. Presently the butler came back.

"The young lady is in a terrible state, sir, and I have sent for Dr. Thomas."

Tarling nodded.

"You have done very wisely," he said. "Poor girl, she has had a terrible shock."

Again he went to the telephone, and this time he got into connection with a nursing home in London and arranged for an ambulance to pick up the girl without further delay. When he had telephoned to Scotland Yard he had asked as an after-thought that a messenger should be sent to Ling Chu, instructing him to come without delay. He had the greatest faith in the Chinaman, particularly in a case like this where the trail was fresh, for Ling Chu was possessed of super-human gifts which only the blood-hound could rival.

"Nobody must go upstairs," he instructed the butler. "When the doctor and the coroner's officer come, they must be admitted by the principal entrance, and if I am not here, you must understand that under no circumstances are those stairs leading to the portico to be used."

He himself went out of the main entrance to make a tour of the grounds. He had little hope that that search would lead to anything. Clues there might be in plenty when the daylight revealed them, but the likelihood of the murderer remaining in the vicinity of the scene of his crime was a remote one.

The grounds were extensive and well-wooded. Numerous winding paths met, and forked aimlessly, radiating out from the broad gravel paths about the house to the high walls which encircled the little estate.

In one corner of the grounds was a fairly large patch, innocent of bush and offering no cover at all. He made a casual survey of this, sweeping his light across the ordered rows of growing vegetables, and was going away when he saw a black bulk which had the appearance, even in the darkness, of a gardener's house. He swept this possible cover with his lamp.

Was his imagination playing him a trick, or had he caught the briefest glimpse of a white face peering round the corner? He put on his light again. There was nothing visible. He walked to the building and round it. There was nobody in sight. He thought he saw a dark form under the shadow of the building moving towards the belt of pines which surrounded the house on the three sides. He put on his lamp again, but the light was not powerful enough to carry the distance required, and he went forward at a jog trot in the direction he had seen the figure disappear. He reached the pines and went softly. Every now and again he stopped, and once he could have sworn he heard the cracking of a twig ahead of him.

He started off at a run in pursuit, and now there was no mistaking the fact that somebody was still in the wood. He heard the quick steps of his quarry and then there was silence. He ran on, but must have overshot the mark, for presently he heard a stealthy noise behind him. In a flash he turned back.

"Who are you?" he said. "Stand out or I'll fire!"

There was no answer and he waited. He heard the scraping of a boot against the brick-work and he knew that the intruder was climbing the wall. He turned in the direction of the sound, but again found nothing.

Then from somewhere above him came such a trill of demoniacal laughter as chilled his blood. The top of the wall was concealed by the overhanging branch of a tree and his light was valueless.

"Come down," he shouted, "I've got you covered!"

Again came that terrible laugh, half-fear, half-derision, and a voice shrill and harsh came down to him.

"Murderer! Murderer! You killed Thornton Lyne, damn you! I've kept this for you — take it!"

Something came crashing through the trees, something small and round, a splashing drop, as of water, fell on the back of Tarling's hand and he shook it off with a cry, for it burnt like fire. He heard the mysterious stranger drop from the coping of the wall and the sound of his swift feet. He stooped and picked up the article which had been thrown at him. It was a small bottle bearing a stained chemist's label and the word "Vitriol."