‘That,’ said Hemingway, ‘is what we are now going to discover.’

‘Well, I hope you’re right, sir; but we’ve been at it the best part of two days now, and we’re no nearer discovery, not as far as I know. Every line we had, or thought we had, broke down. The door-key hadn’t been tampered with; the ladder couldn’t have been got at; and there isn’t a secret way into the room. I’m blessed if I know how we’re ever going to make any headway.’

‘That’s right,’ said Hemingway cheerfully. ‘And all the time I wouldn’t be a bit surprised if the clue to the whole mystery has been under our noses from the outset. Probably something so simple that a child could have spotted it. Life’s like that.’

‘If it’s as simple an all that it’s a wonder you haven’t spotted it,’ said the Sergeant sceptically.

‘It’s very likely too simple for me,’ Hemingway explained. ‘I was hoping you’d hit on it.’

The Sergeant ignored this. ‘If only we had some finger-prints to help us!’ he said. ‘But everything was gone over so carefully, it doesn’t seem to be any use trying that line again. I did think we might have got something from the dagger, but the hilt was as clean as a whistle. And it was plain the other dagger hadn’t been touched, nor the sheath of the one he used. Well, we saw how easily it slipped in and out of the sheath, didn’t we? I could have drawn the blade out without touching the sheath, if I’d wanted to, when I took the whole thing down. In fact, now I come to think of it, I never used my left hand at all, and I’ll bet he didn’t either.’

‘Just a moment!’ said Hemingway, frowning. ‘I believe you’ve got something!’

‘Got what, sir?’

‘Your left hand. Do you remember just what you did do with it when you were up on that chair?’

‘I didn’t do anything with it, barring –’ The Sergeant stopped, and his jaw fell. ‘Good lord!’

‘When you stretched up your right hand, to take the knife down, you steadied yourself with your left hand against the wall. And that, my lad, is ten to one what kind Uncle Joseph did too, without thinking about it any more than you did! Come on, we’ve got to get hold of the finger-print boys!’

The Sergeant rose, but he had been thinking deeply, and he said: ‘Hold on a minute, sir! That’s raised a point in my mind. I had to stretch up a good bit to reach that knife. Joseph couldn’t have got near it, not on a chair.’

‘Then he didn’t use a chair,’ replied Hemingway impatiently. ‘I never met anyone like you for trying to throw a spanner in the works!’

‘What did he use, then?’

Behind Inspector Hemingway’s bright gaze his brain moved swiftly. Once more his excellent memory stood him in good stead. ‘Christmas decorations: step-ladder!’ he said. ‘Same one Nathaniel fell over on his way up to dinner. Come on!’