‘You know,’ said Harper warming a little, ‘it’s a proper mystery, this case. Know what I mean, most cases depend on routine. Boil ‘em down and it’s routine that does the trick as a general rule. May do it here, but all the same this is a teaser. I’m satisfied it wasn’t accident but I can’t prove it. When I’m told on good authority that there was cyanide on that dart, and that Mr Watchman died of cyanide in his blood, I say “well, there’s your weapon,” but alongside of this there’s six people, let alone my own investigation, that prove to my satisfaction nobody could have tampered with the dart. But the dart was poisoned. Now, the stuff in the rat hole was in a little china jar. I’ve left it there for you to see. I got another jar of the same brand. They sell some sort of zinc ointment in them and Abel had several; he’s mad on that sort of thing. Now the amount that’s gone from the bottle, which Noggins says was full, is a quarter of an ounce more than the amount the jar holds and Abel swears he filled the jar. The jar was full when we saw it.’

‘Full?’ said Alleyn sharply. ‘When did you see it?’

‘The next morning.’

‘Was the stuff in the jar analysed?’

Harper turned brick-red.

‘No,’ he said. ‘Abel swore he’d filled it and the jar’s only got his prints on it. And, I tell you, it was full.’

‘Have you got the stuff?’

‘Yes. I poured it off and kept it. Seeing there’s a shortage the stuff on the dart must have come from the bottle.’

‘For how long was the bottle uncorked?’

‘What? Oh, he said that when he used it he uncorked the bottle and put it on the shelf above the hole, with the cork beside it. He was very anxious we should know he’d been careful, and he said he didn’t want to handle the cork more than was necessary. He said he was just going to pour the stuff in the jar when he thought he’d put the jar in position first. He did that and then filled it, holding the torch in his other hand. He swears he didn’t spill any and he swears nobody touched the bottle. The others were standing in the doorway.’

‘So the bottle may have been uncorked for a minute or two?’

‘I suppose so. He plugged up the hole with rag before he did anything else. He had the bottle on the floor beside him.’

‘And then?’