As he rose up again, the curtain ever so slightly stirred.

Wogan pretended to have remarked nothing; he stood easily by the window with his eyes upon his letter and his mind busy with guessing what woman his spy might be.

And he remained on purpose for some while in this attitude, designing it as a punishment.
So long as he stood by the window that unknown woman cheek by jowl with him must hold her breath, must never stir, must silently endure an agony of fear at each movement that he made.
At last he moved, and as he turned away he saw something so unexpected that it startled him.

Indeed, for the moment it did more than startle him, it chilled him.

He understood that slight stirring of the curtain.
The woman now held a dagger in her hand, and the point of the blade stuck out and shone in the moonlight like a flame.
Wogan became angry.