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 l............