`He did what?' shouted the chief inspector.
`Oh, yes; I must tell you about that,' Dr Fell said, frowning as though he were a trifle annoyed with himself: `It was Driscoll who stole it. By the way he rummaged on the floor at the side of his chair, and brought up the tool-basket. After fumbling inside it, he produced what he wanted… `by the way, here's the file he used to-sharpen it. It's rather an old file, so you can see the oblique lines in, the dirt-coating where lie sawed at the barbs of the head. And here are the straighter marks to show where he had started effacing the Souvenir de Carcassonne, before somebody stole the bolt from him to use for another purpose… Hadley took the file and turned it over. `Then I asked you, you know, why that engraving hadn't been entirely obliterated, provided the person who had sharpened the bolt was really the murderer. Let's suppose it had been the murderer. He started in to do it, so why in the name of madness didn't he go on? It was obvious that he didn't want the bolt traced, as it would have been and as it was. But he stopped after a neat job on just three letters. It was only when I realized what was up — an explanation provided by those abstruse notes in Driscoll's notebook that I realized it wasn't the murderer's doing at all. It was Driscoll's. He hadn't finished his job of effacing when along came the murderer: who didn't care where the bolt came from, or whose it was. But, actually this bolt was planned as a part of Driscoll's most daring venture.’
`But, good God, what venture?' demanded Hadley. `There's no way to associate it with the hats.'
`Oh yes, there is,' said Dr Fell. `Hadley, who is the man, above all you can think of, who ranks in the popular eye as England's leading jingo? Who is the man who still makes speeches in private life, as he used to do in public life, about thee might, of the sword, the longbow, the crossbow, and the stout hearts of old? Who is always agitating for bigger armaments? Who is for ever attacking the Prime Minister as a dangerous pacifist? Who, at any rate, is inevitably the person Driscoll would think of in that role?'
`You mean — Sir William Bitton….'
`I mean just that,' nodded the doctor. A grin creased up his chins. `And that insane nephew of his had conceived a design which satisfied all the demands of his sensation-loving soul…. He was going to steal Sir William Bitton's hat and nail it with a crossbow bolt to the door of Number 10 Downing Street.'
Hadley was more than shocked. He was genuinely outraged. For a moment he could only splutter; and Dr Fell contemplated him with amiable mockery.
`Look here.' The doctor opened Driscoll's notebook. `See how he's musing about, this scheme. He hasn't quite worked it out yet. All he has is the idea of fastening Sir William's hat with this warlike instrument in some public place. So he writes, inquiringly: "Best place? Tower? But, of course, that won't do; it's much too easy, and a crossbow bolt in the Tower would be as conspicuous as a small bit of coal at Newcastle. However, he's got to have his properties first, and writes, "Track down hat," which is obvious. Then he thinks about Trafalgar Square again, as he inevitably must. But that won't do, because he certainly can't drive his bolt into the stone of the Nelson monument. So he writes, "Unfortunate Trafalgar, can't transfix!" But it wasn't so unfortunate, for his burst of inspiration comes and you note the exclamation points to denote it. He's got it now. He notes down Number 10 home of the Prime Minister. The next, words you can easily see. Is the door made of wood? If it's steel-bound, or something of the sort, the scheme won't work; he doesn't know. He must find out. Is there a hedge, or anything that will screen him from observation while he does it? Are there guards about, as there are likely to be? He doesn't know this, either. It's a long chance, and a risky one; but he's jubilant about the possibility, and he means to find out.'
Dr Fell put down the notebook.
'Thus,' he said, 'I outline to you what I, like Driscoll, intend to call symbolically the Affair of the Rubber Mouse.