He had good reason to be frightened.

There is no offence more serious than espionage in time of war, and by every rule of war he was a spy.

He had pretended to be a German, which he was not, and had been found within the German lines.

It was true, of course, that he had been ordered into headquarters, but that was a trifling point, and, though he had raised it, Fred knew very well that no technicality would save him if the truth about him came out.
Boris understood all this, undoubtedly, quite as well as Fred or the German captain, but he was beside himself.

He felt that Fred had run into this terrible danger because of him, in order to try to rescue him from an imprisonment that, though annoying, was by no means a serious matter.
"Take me instead of him!" he cried, forgetting that with every word he was really making Fred's case worse.