“Then how does he get there?” demanded Koupriane.

“By the window of the room overlooking the Neva.  He has often come that way.  And that is the way he returns also, I am sure.  It is there you can take him if you act with prudence.”

“How do you know he often comes that way?”

“You know the height of the window above the little roadway.  To reach it he uses a water-trough, whose iron rings are bent, and also the marks of a grappling-iron that he carries with him and uses to hoist himself to the window are distinctly visible on the ironwork of the little balcony outside.  The marks are quite obviously of different dates”

“But that window is closed.”

“Someone opens it for him.”

“Who, if you please?”

“I have no desire to know.”

“Eh, yes.  It necessarily is Natacha.  I was sure that the Villa des Iles had its viper.  I tell you she doesn’t dare leave her nest because she knows she is watched.  Not one of her movements outside escapes us!  She knows it.  She has been warned.  The last time she ventured outside alone was to go into the old quarters of Derewnia.  What has she to do in such a rotten quarter?  I ask you that.  And she turned in her tracks without seeing anyone, without knocking at a single door, because she saw that she was followed.  She isn’t able to get to see them outside, therefore she has to see them inside.”

“They are only one, and always the same one.”

“Are you sure?”

“An examination of the marks on the wall and on the pipe doesn’t leave any doubt of it, and it is always the same grappling-iron that is used for the window.”

“The viper!”

“Monsieur Koupriane, Mademoiselle Natacha seems to preoccupy you exceedingly.  I did not come here to talk about Mademoiselle Natacha.  I came to point out to you the route used by the man who comes to do the murder.”

“Eh, yes, it is she who opens the way.”

“I can’t deny that.”

“The little demon!  Why does she take him into her room at night?  Do you think perhaps there is some love-affair...?”

“I am sure of quite the opposite.”

“I too.  Natacha is not a wanton.  Natacha has no heart.  She has only a brain.  And it doesn’t take long for a brain touched by Nihilism to get so it won’t hesitate at anything.”

Koupriane reflected a minute, while Rouletabille watched him in silence.

“Have we solely to do with Nihilism?” resumed Koupriane.  “Everything you tell me inclines me more and more to my idea:  a family affair, purely in the family.  You know, don’t you, that upon the general’s death Natacha will be immensely rich?”

“Yes, I know it,” replied Rouletabille, in a voice that sounded singular to the ear of the Chief of Police and which made him raise his head.

“What do you know?”

“I?  Nothing,” replied the reporter, this time in a firmer tone.  “I ought, however, to say this to you:  I am sure that we are dealing with Nihilism...”