`Proof of what? Dealing in explosives without a licence perhaps.' This was meant for a contemptuous jeer, though the expression of the thin, sickly face remained unchanged, and the utterance was negligent. `I don't think there's one of them anxious to make that arrest. I don't think they could get one of them to apply for a warrant. I mean one of the best. Not one.'

`Why?' Ossipon asked.

`Because they know very well I take care never to part with the last handful of my wares. I've it always by me.' He touched the breast of his coat lightly. `In a thick glass flask,' he added.

`So I have been told,' said Ossipon, with a shade of wonder in his voice. `But I didn't know if...'

`They know,' interrupted the little man, crisply, leaning against the straight chair back, which rose higher than his fragile head. `I shall never be arrested. The game isn't good enough for any policeman of them all. To deal with a man like me you require sheer, naked, inglorious heroism.'

Again his lips closed with a self-confident snap. Ossipon repressed a movement of impatience.

`Or recklessness - or simply ignorance,' he retorted. `They've only to get somebody for the job who does not know you carry enough stuff in your pocket to blow yourself and everything within sixty yards of you to pieces.'

`I never affirmed I could not be eliminated,' rejoined the other. `But that wouldn't be an arrest. Moreover, it's not so easy as it looks.'

`Bah!' Ossipon contradicted. `Don't be too sure of that. What's to prevent half-a-dozen of them jumping upon you from behind in the street? With your arms pinned to your sides you could do nothing - could you?'

`Yes; I could. I am seldom out in the streets after dark,' said the little man, impassively, `and never very late. I walk always with my right hand closed round the india-rubber ball which I have in my trouser pocket. The pressing of this ball actuates a detonator inside the flask I carry in my pocket. It's the principle of the pneumatic instantaneous shutter for a camera lens. The tube leads up...'

With a swift, disclosing gesture he gave Ossipon a glimpse of an india-rubber tube, resembling a slender brown worm, issuing from the armhole of his waistcoat and plunging into the inner breast pocket of his jacket. His clothes, of a nondescript brown mixture, were threadbare and marked with stains, dusty in the folds, with ragged button-holes. `The detonator is partly mechanical, partly chemical,' he explained, with casual condescension.

`It is instantaneous, of course?' murmured Ossipon, with a slight shudder.

`Far from it,' confessed the other, with a reluctance which seemed to twist his mouth dolorously. `A full twenty seconds must elapse from the moment I press the ball till the explosion takes place.'

`Phew!' whistled Ossipon, completely appalled. `Twenty seconds! Horrors! You mean to say that you could face that? I should go crazy...'

`Wouldn't matter if you did. Of course, it's the weak point of this special system, which is only for my own use. The worst is that the manner of exploding is always the weak point with us. I am trying to invent a detonator that would adjust itself to all conditions of action, and even to unexpected changes of conditions. A variable and yet perfectly precise mechanism. A really intelligent detonator.'

`Twenty seconds,' muttered Ossipon again. `Ough! And then...'