‘Looks like it!’ ejaculated Harper. ‘It blasted well shrieks of it. I’m a hell of a detective I am! Look at me! I missed the point about that evaporation business! Took Abel in to look at the pot and he said it was just the amount he’d poured in. Well, the damn thing was full. I never thought it might be water. I took photographs and sealed the place up just as it was. I did pour off this stuff and keep it. I’ll say that for myself. I made sure the poison had come out of the bottle in the cupboard. Blast it!’

‘Abel’s prints,’ Alleyn said, ‘were still on the key of the cupboard and on the knob. You can’t open the door without turning the key and the knob. Dr Shaw saw that, when he looked at the cupboard and waited until it had been tested for prints. If anyone else had been to the cupboard they would either have left their own prints, used gloves and smeared Abel’s prints, or else wiped them off entirely. Nobody could have been to the cupboard.’

‘I knew that, but all the same—Well, I suppose I thought they might have got at the bottle while—oh, hell!’

‘Anybody might have missed it, Mr Harper,’ said Fox. ‘I didn’t pick it till Mr Alleyn pointed it out.’

‘And I was lucky,’ said Alleyn. ‘I’d read Taylor on the cyanides during our trip down.’

‘Well,’ said Harper, ‘the coroner and Dr Shaw missed the point. Oates gave evidence of discovery of the stuff in the rat-hole. Old Pomeroy deposed it was the same amount he’d poured in. Nobody said anything about evaporation.’

‘Oates,’ Alleyn pointed out, ‘saw it the first night with Dr Shaw, before they knew the exact nature of the poison. Not much more than twenty-six hours after it was put there.’

‘He might have just dipped the dart in the stuff,’ said Harper. ‘I did think of that. But now—’

‘Now we know the dart must have been doctored a very short time before Oates sealed it up. You see where we’re heading?’

‘Yes,’ said Harper unwillingly. ‘I see, all right. But suppose Legge had the stuff on him and put it on the dart just before he threw it—’