He leaned forward and tapped me on the knee.  ’I reverence the British Intelligence Service.  Flies don’t settle on it to any considerable extent.  It’s got a mighty fine mesh, but there’s one hole in that mesh, and it’s our job to mend it.  There’s a high-powered brain in the game against us.  I struck it a couple of years ago when I was hunting Dumba and Albert, and I thought it was in Noo York, but it wasn’t.  I struck its working again at home last year and located its head office in Europe.  So I tried Switzerland and Holland, but only bits of it were there.  The centre of the web where the old spider sits is right here in England, and for six months I’ve been shadowing that spider.  There’s a gang to help, a big gang, and a clever gang, and partly an innocent gang.  But there’s only one brain, and it’s to match that that the Robson Brothers settled my duodenum.’

I was listening with a quickened pulse, for now at last I was getting to business.

‘What is he—­international socialist, or anarchist, or what?’ I asked.

’Pure-blooded Boche agent, but the biggest-sized brand in the catalogue—­bigger than Steinmeier or old Bismarck’s Staubier.  Thank God I’ve got him located . . .  I must put you wise about some things.’

He lay back in his rubbed leather armchair and yarned for twenty minutes.  He told me how at the beginning of the war Scotland Yard had had a pretty complete register of enemy spies, and without making any fuss had just tidied them away.  After that, the covey having been broken up, it was a question of picking off stray birds.  That had taken some doing.  There had been all kinds of inflammatory stuff around, Red Masons and international anarchists, and, worst of all, international finance-touts, but they had mostly been ordinary cranks and rogues, the tools of the Boche agents rather than agents themselves.  However, by the middle of 1915 most of the stragglers had been gathered in.  But there remained loose ends, and towards the close of last year somebody was very busy combining these ends into a net.  Funny cases cropped up of the leakage of vital information.  They began to be bad about October 1916, when the Hun submarines started on a special racket.  The enemy suddenly appeared possessed of a knowledge which we thought to be shared only by half a dozen officers.  Blenkiron said he was not surprised at the leakage, for there’s always a lot of people who hear things they oughtn’t to.  What surprised him was that it got so quickly to the enemy.

Then after last February, when the Hun submarines went in for frightfulness on a big scale, the thing grew desperate.  Leakages occurred every week, and the business was managed by people who knew their way about, for they avoided all the traps set for them, and when bogus news was released on purpose, they never sent it.  A convoy which had been kept a deadly secret would be attacked at the one place where it was helpless.  A carefully prepared defensive