The three of us went back towards the pavilion. At some distance from the building the reporter made us stop and, pointing to a small clump of trees to the right of us, said:

“That’s where the murderer came from to get into the pavilion.”

As there were other patches of trees of the same sort between the great oaks, I asked why the murderer had chosen that one, rather than any of the others. Rouletabille answered me by pointing to the path which ran quite close to the thicket to the door of the pavilion.

“That path is as you see, topped with gravel,” he said; “the man must have passed along it going to the pavilion, since no traces of his steps have been found on the soft ground. The man didn’t have wings; he walked; but he walked on the gravel which left no impression of his tread. The gravel has, in fact, been trodden by many other feet, since the path is the most direct way between the pavilion and the chateau. As to the thicket, made of the sort of shrubs that don’t flourish in the rough season—laurels and fuchsias—it offered the murderer a sufficient hiding-place until it was time for him to make his way to the pavilion. It was while hiding in that clump of trees that he saw Monsieur and Mademoiselle Stangerson, and then Daddy Jacques, leave the pavilion. Gravel has been spread nearly, very nearly, up to the windows of the pavilion. The footprints of a man, parallel with the wall—marks which we will examine presently, and which I have already seen—prove that he only needed to make one stride to find himself in front of the vestibule window, left open by Daddy Jacques. The man drew himself up by his hands and entered the vestibule.”

“After all it is very possible,” I said.

“After all what? After all what?” cried Rouletabille.

I begged of him not to be angry; but he was too much irritated to listen to me and declared, ironically, that he admired the prudent doubt with which certain people approached the most simple problems, risking nothing by saying “that is so, or ‘that is not so.” Their intelligence would have produced about the same result if nature had forgotten to furnish their brain-pan with a little grey matter. As I appeared vexed, my young friend took me by the arm and admitted that he had not meant that for me; he thought more of me than that.

“If I did not reason as I do in regard to this gravel,” he went on, “I should have to assume a balloon!—My dear fellow, the science of the aerostation of dirigible balloons is not yet developed enough for me to consider it and suppose that a murderer would drop from the clouds! So don’t say a thing is possible, when it could not be otherwise. We know now how the man entered by the window, and we also know the moment at which he entered,—during the five o’clock walk of the professor and his daughter. The fact of the presence of the chambermaid—who had come to clean up The Yellow Room—in the laboratory, when Monsieur Stangerson and his daughter returned from their walk, at half-past one, permits us to affirm that at half-past one the murderer was not in the chamber under the bed, unless he was in collusion with the chambermaid. What do you say, Monsieur Darzac?”

Monsieur Darzac shook his head and said he was sure of the chambermaid’s fidelity, and that she was a thoroughly honest and devoted servant.

“Besides,” he added, “at five o’clock Monsieur Stangerson went into the room to fetch his daughter’s hat.”

“There is that also,” said Rouletabille.

“That the man entered by the window at the time you say, I admit,” I said; “but why did he shut the window? It was an act which would necessarily draw the attention of those who had left it open.”

“It may be the window was not shut at once,” replied the young reporter. “But if he did shut the window, it was because of the bend in the gravel path, a dozen yards from the pavilion, and on account of the three oaks that are growing at that spot.”

“What do you mean by that?” asked Monsieur Darzac, who had followed us and listened with almost breathless attention to all that Rouletabille had said.

“I’ll explain all to you later on, Monsieur, when I think the moment to be ripe for doing so; but I don’t think I have anything of more importance to say on this affair, if my hypothesis is justified.”

“And what is your hypothesis?”

“You will never know if it does not turn out to be the truth. It is of much too grave a nature to speak of it, so long as it continues to be only a hypothesis.”

“Have you, at least, some idea as to who the murderer is?”

“No, monsieur, I don’t know who the murderer is; but don’t be afraid, Monsieur Robert Darzac—I shall know.”

I could not but observe that Monsieur Darzac was deeply moved; and I suspected that Rouletabille’s confident assertion was not pleasing to him. Why, I asked myself, if he was really afraid that the murderer should be discovered, was he helping the reporter to find him? My young friend seemed to have received the same impression, for he said, bluntly:

“Monsieur Darzac, don’t you want me to find out who the murderer was?”

“Oh!—I should like to kill him with my own hand!” cried Mademoiselle Stangerson’s fiance, with a vehemence that amazed me.

“I believe you,” said Rouletabille gravely; “but you have not answered my question.”

We were passing by the thicket, of which the young reporter had spoken to us a minute before. I entered it and pointed out evident traces of a man who had been hidden there. Rouletabille, once more, was right.

“Yes, yes!” he said. “We have to do with a thing of flesh and blood, who uses the same means that we do. It’ll all come out on those lines.”

Having said this, he asked me for the paper pattern of the footprint which he had given me to take care of, and applied it to a very clear footmark behind the thicket. “Aha!” he said, rising.

I thought he was now going to trace back the track of the murderer’s footmarks to the vestibule window; but he led us instead, far to the left, saying that it was useless ferreting in the mud, and that he was sure, now, of the road taken by the murderer.

“He went along the wall to the hedge and dry ditch, over which he jumped. See, just in front of the little path leading to the lake, that was his nearest way to get out.”

“How do you know he went to the lake?”—

“Because Frederic Larsan has not quitted the borders of it since this morning. There must be some important marks there.”

A few minutes later we reached the lake.

It was a little sheet of marshy water, surrounded by reeds, on which floated some dead water-lily leaves. The great Fred may have seen us approaching, but we probably interested him very little, for he took hardly any notice of us and continued to be stirring with his cane something which we could not see.

“Look!” said Rouletabille, “here again are the footmarks of the escaping man; they skirt the lake here and finally disappear just before this path, which leads to the high road to Epinay. The man continued his flight to Paris.”

“What makes you think that?” I asked, “since these footmarks are not continued on the path?”

“What makes me think that?—Why these footprints, which I expected to find!” he cried, pointing to the sharply outlined imprint of a neat boot. “See!”—and he called to Frederic Larsan.

“Monsieur Fred, these neat footprints seem to have been made since the discovery of t............