With trembling hands I tied up the bag again, rolled it in a newspaper, and stuffed it into my pocket.  For I remembered a day near Peronne when a Boche plane had come over in the night and had dropped little bags like this.  Happily they were all collected, and the men who found them were wise and took them off to the nearest laboratory.  They proved to be full of anthrax germs . . .

I remembered how Eaucourt Sainte-Anne stood at the junction of a dozen roads where all day long troops passed to and from the lines.  From such a vantage ground an enemy could wreck the health of an army . . .

I remembered the woman I had seen in the courtyard of this house in the foggy dusk, and I knew now why she had worn a gas-mask.

This discovery gave me a horrid shock.  I was brought down with a crash from my high sentiment to something earthly and devilish.  I was fairly well used to Boche filthiness, but this seemed too grim a piece of the utterly damnable.  I wanted to have Ivery by the throat and force the stuff into his body, and watch him decay slowly into the horror he had contrived for honest men.

‘Let’s get out of this infernal place,’ I said.

But Mary was not listening.  She had picked up one of the newspapers and was gloating over it.  I looked and saw that it was open at an advertisement of Weissmann’s ‘Deep-breathing’ system.

‘Oh, look, Dick,’ she cried breathlessly.

The column of type had little dots made by a red pencil below certain words.

‘It’s it,’ she whispered, ’it’s the cipher—­I’m almost sure it’s the cipher!’

‘Well, he’d be likely to know it if anyone did.’

’But don’t you see it’s the cipher which Chelius uses—­the man in Switzerland?  Oh, I can’t explain now, for it’s very long, but I think—­I think—­I have found out what we have all been wanting.  Chelius . . .’

‘Whisht!’ I said.  ‘What’s that?’

There was a queer sound from the out-of-doors as if a sudden wind had risen in the still night.

‘It’s only a car on the main road,’ said Mary.

‘How did you get in?’ I asked.

’By the broken window in the next room.  I cycled out here one morning, and walked round the place and found the broken catch.’

’Perhaps it is left open on purpose.  That may be the way M. Bommaerts visits his country home . . .  Let’s get off, Mary, for this place has a curse on it.  It deserves fire from heaven.’

I slipped the contents of the attache case into my pockets.  ’I’m going to drive you back,’ I said.  ‘I’ve got a car out there.’

’Then you must take my bicycle and my servant too.  He’s an old friend of yours—­one Andrew Amos.’

‘Now how on earth did Andrew get over here?’

‘He’s one of us,’ said Mary, laughing at my surprise.  ’A most useful member of our party, at present disguised as an infirmier in Lady Manorwater’s Hospital at Douvecourt.  He is learning French, and . . .’