‘I considered the time had come,’ he said, ’to pay high for valuable noos, so I sold the enemy a very pretty de-vice.  If you ever gave your mind to ciphers and illicit correspondence, Dick, you would know that the one kind of document you can’t write on in invisible ink is a coated paper, the kind they use in the weeklies to print photographs of leading actresses and the stately homes of England.  Anything wet that touches it corrugates the surface a little, and you can tell with a microscope if someone’s been playing at it.  Well, we had the good fortune to discover just how to get over that little difficulty—­how to write on glazed paper with a quill so as the cutest analyst couldn’t spot it, and likewise how to detect the writing.  I decided to sacrifice that invention, casting my bread upon the waters and looking for a good-sized bakery in return . . .  I had it sold to the enemy.  The job wanted delicate handling, but the tenth man from me—­he was an Austrian Jew—­did the deal and scooped fifty thousand dollars out of it.  Then I lay low to watch how my friend would use the de-vice, and I didn’t wait long.’

He took from his pocket a folded sheet of L’Illustration.  Over a photogravure plate ran some words in a large sprawling hand, as if written with a brush.

‘That page when I got it yesterday,’ he said, ’was an unassuming picture of General Petain presenting military medals.  There wasn’t a scratch or a ripple on its surface.  But I got busy with it, and see there!’

He pointed out two names.  The writing was a set of key-words we did not know, but two names stood out which I knew too well.  They were ‘Bommaerts’ and ‘Chelius’.

‘My God!’ I cried, ’that’s uncanny.  It only shows that if you chew long enough—–­’

‘Dick,’ said Mary, ’you mustn’t say that again.  At the best it’s an ugly metaphor, and you’re making it a platitude.’

‘Who is Ivery anyhow?’ I asked.  ’Do you know more about him than we knew in the summer?  Mary, what did Bommaerts pretend to be?’

‘An Englishman.’  Mary spoke in the most matter-of-fact tone, as if it were a perfectly usual thing to be made love to by a spy, and that rather soothed my annoyance.  ’When he asked me to marry him he proposed to take me to a country-house in Devonshire.  I rather think, too, he had a place in Scotland.  But of course he’s a German.’

‘Ye-es,’ said Blenkiron slowly, ’I’ve got on to his record, and it isn’t a pretty story.  It’s taken some working out, but I’ve got all the links tested now . . .  He’s a Boche and a large-sized nobleman in his own state.  Did you ever hear of the Graf von Schwabing?’

I shook my head.

‘I think I have heard Uncle Charlie speak of him,’ said Mary, wrinkling her brows.  ‘He used to hunt with the Pytchley.’