Fox opened Alleyn’s bag. From it he took two open-mouthed vessels about two inches high, two watch-glasses, and a small bottle. Alleyn squinted at the bottle.

‘Silver nitrate. That’s the stuff. Can you produce some warm water, Nick? Well, well, I am exceeding my duty to be sure.’

Harper went out and returned with a jug of water and a photographic dish. Alleyn poured a little water into the dish, half-filled one of his tiny vessels with the fluid found in the rat-hole, and the other with acid from Abel’s bottle. He wetted the underside of the watch-glasses with nitrate solution and placed them over the vessels. He then stood the vessels, closed by the watch-glasses, in the warm water.

‘Fox now says the Lord’s Prayer backwards,’ he explained. ‘I emit a few oddments of ectoplasm and Hi Cockalorum the spell is wound up! Take a look at that, Nick.’

They stared at the dish. On the surface of the prussic acid a little spiral had risen. It became denser, it flocculated and the watch-glass was no longer transparent but covered with an opaque whiteness.

‘That’s cyanide, that was,’ said Alleyn. ‘Now, look at the other. A blank, my lord. It’s water, Br’er Fox, it’s water. Now let’s pour them back into their respective bottles and don’t give me away to the analyst.’

‘I suppose,’ said Harper, as Alleyn tidied up. ‘I suppose this means we needn’t worry ourselves about the cupboard. The cupboard doesn’t come into the blasted affair.’

Alleyn held on the palm of his hand the three pieces of glass he had separated from the fragments of the broken brandy tumbler, and the small misshapen lumps he had found in the ashes of the fire.

‘Oh, yes,’ he said. ‘Yes. We’re not home yet, not by a long march, but the cupboard still comes into the picture. Think.’

Harper looked from the pieces of glass to Alleyn’s face and back again.

‘Yes,’ he said slowly, ‘yes. But you’ll have the devil of a job to prove it.’

‘I agree,’ said Alleyn. ‘Nevertheless, Nick, I hope to prove it.’

CHAPTER 17
Mr Fox Takes Sherry

Parish came downstairs singing ‘La Donna è Mobile’. He had a pleasant baritone voice which had been half-trained in the days when he had contemplated musical comedy. He sang stylishly and one could not believe that he sang unconsciously. He swung open the door of the private tap and entered on the last flourish of that impertinent, that complacently debonair refrain.

‘Good evening, sir,’ said Abel from behind the bar. ‘‘Tis again.’

Parish smiled wistfully.

‘Ah, Abel,’ he said with a slight sigh, ‘it’s not as easy as it sounds; but my cousin would have been the last man to want long faces, poor dear old fellow.’

‘So he would, then,’ rejoined Abel heartily, ‘the very last.’