‘Not having his brains, his memory, or his library, I can’t tell you,’ said Dr Shaw.

III

Alleyn, Fox and Harper went to the police station. Here they had a long reiterative conversation. They compared Alleyn’s casts with the shoes Watchman wore on the day of his death, and found that they tallied exactly. They went over the case step by step. Alleyn expounded, the others listened. They laid their collection of oddments on Harper’s table; the brandy-bottle, the broken glass, the iodine bottle, the stained newspaper, the small china vessel from the rat-hole and the bottle of Scheele’s Acid. Harper gave Alleyn a stoppered bottle.

‘Ah,’ said Alleyn, ‘that’s the stuff out of the rat-hole jar. I want you to get it analysed. Perhaps Dr Mordant would do it. No, I suppose that would be too unofficial. It had better go up to London.’

‘You think our murderer got the stuff from the garage?’ asked Harper.

‘I do.’

‘But the thing was full.’

‘Because it was full,’ said Alleyn.

‘You reckon that was water,’ asked Harper slowly.

‘Yes, Nick.’

‘I see,’ said Harper.

‘The poison-party,’ said Alleyn, ‘was attended by Abel, who put the prussic acid in the china pot and stopped the hole; by Will, by Miss Moore, by Legge, who only looked in for a moment, and by a couple of fishermen who were on their way to the public bar and who don’t come into the picture. Subsequently Abel warned everybody in the place about what he had done, so that the actual attendance at the poison-party may not give us our answer. On the other hand it is possible that one of them lagged behind and pinched the poison. They all profess to have forgotten in what order they left. Now prussic acid in Mr Noggins’ fifty per cent solution is a highly volatile liquid. Judging by the stench, its fumes have accounted for at least one rat, so probably it was not removed immediately. On the other hand it seems it would evaporate considerably in something under an hour. I’m not sure on this point. We’ll experiment. The experts say in their report, under an hour. Very good. My contention is that the murderer must have nipped into the garage, within an hour after Abel left it, and taken the poison which would be kept in a tightly-corked bottle until it was needed.’

‘But how the hell would he get it? The jar had Abel’s prints. It hadn’t been touched.’

‘Do you remember—?’

‘By God!’ shouted Harper. ‘Don’t tell me. I’ve got it.’

He broke into a stream of oaths through which his enlightenment struggled for expression.

‘That’s it,’ said Alleyn. ‘Looks like it, doesn’t it?’