All that remained of the once stately, if restricted, premises of Messrs. Dashwood and Solomon was a gaunt-looking front wall, blackened by the fire. Tarling interviewed the Chief of the Fire Brigade.

"It'll be days before we can get inside," said that worthy, "and I very much doubt if there's anything left intact. The whole of the building has been burnt out—you can see for yourself the roof has gone in—and there's very little chance of recovering anything of an inflammable nature unless it happens to be in a safe."

Tarling caught sight of the brusque Sir Felix Solomon gazing, without any visible evidence of distress, upon the wreckage of his office.

"We are covered by insurance," said Sir Felix philosophically, "and there is nothing of any great importance, except, of course, those documents and books from Lyne's Store."

"They weren't in the fire-proof vault?" asked Tarling, and Sir Felix shook his head.

"No," he said, "they were in a strong-room; and curiously enough, it was in that strong room where the fire originated. The room itself was not fire-proof, and it would have been precious little use if it had been, as the fire started inside. The first news we received was when a clerk, going down to the basement, saw flames leaping out between the steel bars which constitute the door of No. 4 vault."

Tarling nodded.

"I need not ask you whether the books which Mr. Milburgh brought this morning had been placed in that safe, Sir Felix," he said, and the knight looked surprised.

"Of course not. They were placed there whilst you were in the office," he said. "Why do you ask?"

"Because in my judgment those books were not books at all in the usually understood sense. Unless I am at fault, the parcel contained three big ledgers glued together, the contents being hollowed out and that hollow filled with thermite, a clockwork detonator, or the necessary electric apparatus to start a spark at a given moment."

The accountant stared at him.

"You're joking," he said, but Tarling shook his head.

"I was never more serious in my life."

"But who would commit such an infernal act as that? Why, one of my clerks was nearly burnt to death!"

"The man who would commit such an infernal act as that," repeated Tarling slowly, "is the man who has every reason for wishing to avoid an examination of Lyne's accounts."

"You don't mean——?"

"I'll mention no names for the moment, and if inadvertently I have conveyed the identity of the gentleman of whom I have been speaking, I hope you will be good enough to regard it as confidential," said Tarling, and went back to his crestfallen subordinate.

"No wonder Milburgh was satisfied with the forthcoming examination," he said bitterly. "The devil had planted that parcel, and had timed it probably to the minute. Well, there's nothing more to be done to-night—with Milburgh."

He looked at his watch.

"I'm going back to my flat, and afterwards to Hertford," he said.

He had made no definite plan as to what line he should pursue after he reached Hertford. He had a dim notion that his investigation hereabouts might, if properly directed, lead him nearer to the heart of the mystery. This pretty, faded woman who lived in such style, and whose husband was so seldom visible, might give him a key. Somewhere it was in existence, that key, by which he could decipher the jumbled code of the Daffodil Murder, and it might as well be at Hertford as nearer at hand.

It was dark when he came to the home of Mrs. Rider, for this time he had dispensed with a cab, and had walked the long distance between the station and the house, desiring to avoid attention. The dwelling stood on the main road. It had a high wall frontage of about three hundred and fifty feet. The wall was continued down the side of a lane, and at the other end marked the boundary of a big paddock.

The entrance to the grounds was through a wrought-iron gate of strength, the design of which recalled something which he had seen before. On his previous visit the gate had been unfastened, and he had had no difficulty in reaching the house. Now, however, it was locked.

He put his flashlight over the gate and the supporting piers, and discovered a bell, evidently brand new, and recently fixed. He made no attempt to press the little white button, but continued his reconnaissance. About half-a-dozen yards inside the gateway was a small cottage, from which a light showed, and apparently the bell communicated with this dwelling. Whilst he was waiting, he heard a whistle and a quick footstep coming up the road, and drew into the shadow. Somebody came to the gate; he heard the faint tinkle of a bell and a door opened.

The new-comer was a newspaper boy, who pushed a bundle of evening papers through the iron bars and went off again. Tarling waited until he heard the door of the cottage or lodge close. Then he made a circuit of the house, hoping to find another entrance. There was evidently a servants' entrance at the back, leading from the lane, but this too was closed. Throwing his light up, he saw that there was no broken glass on top of the wall, as there had been in the front of the house, and, making a jump, he caught the stone coping and drew himself up and astride.

He dropped into the darkness on the other side without any discomfort to himself, and made his cautious way towards the house. Dogs were the danger, but apparently Mrs. Rider did not keep dogs, and his progress was unchallenged.

He saw no light either in the upper or lower windows until he got to the back. Here was a pillared-porch, above which had been built what appeared to be a conservatory. Beneath the porch was a door and a barred window, but it was from the conservatory above that a faint light emanated. He looked round for a ladder without success. But the portico presented no more difficulties than the wall had done. By stepping on to the window-sill and steadying himself against one of the pillars, he could reach an iron stanchion, which had evidently been placed to support the framework of the superstructure. From here to the parapet of the conservatory itself was but a swing. This glass-house had casement windows, one of which was open, and he leaned on his elbows and cautiously intruded his head.

The place was empty. The light came from an inner room opening into the glass sheltered balcony. Quickly he slipped through the windows and crouched under the shadow of a big oleander. The atmosphere of the conservatory was close and the smell was earthy. He judged from the hot-water pipes which his groping hands felt that it was a tiny winter garden erected by the owner of the house for her enjoyment in the dark, cold days. French windows admitted to the inner room, and, peering through the casement curtains which covered them, Tarling saw Mrs. Rider. She was sitting at a desk, a pen in her hand, her chin on her finger-tips. She was not writing, but staring blankly at the wall, as though she were at a loss for what to say.

The light came from a big alabaster bowl hanging a foot below the ceiling level, and it gave the detective an opportunity of making a swift examination. The room was furnished simply if in perfect taste, and had the appearance of a study. Beside her desk was a green safe, half let into the wall and half exposed. There were a few prints hanging on the walls, a chair or two, a couch half hidden from the detective's view, and that was all. He had expected to see Odette Rider with her mother, and was disappointed. Not only was Mrs. Rider alone, but she conveyed the impression that she was practically alone in the house.

Tarling knelt, watching her, for ten minutes, until he heard a sound outside. He crept softly back and looked over the edge of the portico in time to see a figure moving swiftly along the path. It was riding a bicycle which did not carry a light. Though he strained his eyes, he could not tell whether the rider was man or woman. It disappeared under the portico and he heard the grating of the machine as it was leant against one of the pillars, the click of a key in the lock and the sound of a door opening. Then he crept back to his observation post overlooking the study.

Mrs. Rider had evidently not heard the sound of the door opening below, and sat without movement still staring at the wall before her. Presently she started and looked round towards the door. Tarling noted the door—noted, too the electric switch just in view. Then the door opened slowly. He saw Mrs. Rider's face light up with pleasure, then somebody asked a question in a whisper, and she answered—he could just hear her words:

"No darling, nobody."

Tarling held his breath and waited. Then, of a sudden, the light in the room was extinguished. Whoever had entered had turned out the light. He heard a soft footfall coming towards the window looking into the conservatory and the rattle of the blinds as they were lowered. Then the light went up again, but he could see nothing or hear nothing.

Who was Mrs. Rider's mysterious visitor? There was only one way to discover, but he waited a little longer—waited, in fact, until he heard the soft slam of a safe door closing—before he slipped again through the window and dropped to the ground.

The bicycle was, as he had expected, leaning against one of the pillars. He could see nothing, and did not dare flash his lamp, but his sensitive fingers ran over its lines, and he barely checked an exclamation of surprise. It was a lady's bicycle!

He waited a little while, then withdrew to a shrubbery opposite the door on the other side of the drive up which the cyclist had come. He had not long to wait before the door under the portico opened again and closed. Somebody jumped on to the bicycle as Tarling leaped from his place of concealment. He pressed the key of his electric lamp, but for some reason it did not act. He felt rather than heard a shiver of surprise from the person on the machine.

"I want you," said Tarling, and put out his hands.

He missed the rider by the fraction of an inch, but saw the machine swerve and heard the soft thud of something falling. A second later the machine and rider had disappeared in the pitch darkness.

He re-fixed his lamp. Pursuit, he knew, was useless without his lantern, and, cursing the maker thereof, he adjusted another battery, and put the light on the ground to see what it was that the fugitive had dropped. He thought he heard a smothered exclamation behind him and turned swiftly. But nobody came within the radius of his lamp. He must be getting nervy, he thought, and continued his inspection of the wallet.

It was a long, leather portfolio, about ten inches in length and five inches in depth, and it was strangely heavy. He picked it up, felt for the clasp, and found instead two tiny locks. He made another examination by the light of his lantern, an examination which was interrupted by a challenge from above.

"Who are you?"

It was Mrs. Rider's voice, and just then it was inconvenient for him to reveal himself. Without a word in answer, he switched off his light and slipped into the bushes, and, more as the result of instinct than judgment, regained the wall, at almost the exact spot he had crossed it.

The road was empty, and there was no sign of the cyclist. There was only one thing to do and that was to get back to town as quickly as possible and examine the contents of the wallet at his leisure. It was extraordinary heavy for its size, he was reminded of that fact by his sagging pocket.

The road back to Hertford seemed interminable and the clocks were chiming a quarter of eleven when he entered the station yard.

"Train to London, sir?" said the porter. "You've missed the last train to London by five minutes!"