They were dreading nothing so much as the chance of Monsieur Stangerson knowing that his daughter was 'held' by her assailant.

I made Monsieur Darzac understand that he had explained himself sufficiently, and that he might refrain from telling me any more than he had already told me.

I promised him to watch through the night.

He insisted that I should establish an absolutely impassable barrier around Mademoiselle Stangerson's chamber, around the boudoir where the nurses were sleeping, and around the drawing-room where, since the affair of the inexplicable gallery, Monsieur Stangerson had slept.

In short, I was to put a cordon round the whole apartment.
"From his insistence I gathered that Monsieur Darzac intended not only to make it impossible for the expected man to reach the chamber of Mademoiselle Stangerson, but to make that impossibility so visibly clear that, seeing himself expected, he would at once go away.