‘Come to think of it,’ objected the Sergeant, ‘that doesn’t point particularly to Miss Herriard. He wouldn’t suspect any of the people in the house, would he?’

‘He’d suspect them fast enough if they started tampering with the lock of his door,’ said Hemingway. ‘No, it looks as though the murderer came in in the natural way, all aboveboard and open, stabbed the old man, and went out again, locking the door behind him by some means which we haven’t yet discovered. And somehow I don’t believe it.’

The Sergeant saw the frown on his superior’s brow, and asked: ‘Why not, sir?’

‘I’ve got a feeling it didn’t happen that way. What did the murderer lock the door for at all? It’s no use saying, to bamboozle the police, because it isn’t good enough. If you find a corpse in a locked room, what’s the inference?’

‘Suicide,’ replied the Sergeant promptly.

‘Exactly. And if you want a murder to look like suicide you don’t first stab the victim in the back, and next remove the knife. There was no idea of making this look like suicide, so the locked door doesn’t add up at all.’ He looked carefully at the plate in the jamb, which had been torn away. ‘In fact,’ he said, ‘I’m beginning to wonder whether the door ever was locked.’

The Sergeant weighed this suggestion on its merits. ‘Three of them said that it was.’

‘Four, counting Miss Herriard,’ agreed Hemingway.

‘Four’s too many to be in a conspiracy,’ said the Sergeant positively.

‘The valet said that he couldn’t get any answer to his knock. I don’t recall that he said he had tried the door.’

‘You mean,’ said the Sergeant slowly, ‘that you think maybe he only knocked, and when Stephen Herriard came up it was he who forced the latch, and turned the key quickly afterwards, when no one was looking?’

‘I don’t think anything of the kind,’ said Hemingway. ‘I have got an open mind.’

‘What did you make of the cigarette-case, sir?’

‘It doesn’t look too good for Master Stephen, on the face of it.’

‘No; but that’s complicated too, isn’t it, sir? I mean, there seems to be plenty of evidence to show that the last person known to be in possession of the case was Miss Dean.’

‘Look here!’ said Hemingway. ‘I can accept the theory that Stephen walked in here to have a quiet chat with his uncle over a cigarette (though, mark you, on the evidence it doesn’t seem likely), but what I can’t swallow is the suggestion that Miss Dean did. Get hold of the valet for me, will you?’

Ford, when he presently appeared in the Sergeant’s wake, showed a slight reluctance to enter the room, and seemed a little nervous. Detectives from Scotland Yard were outside the range of his experience, and although he could look Inspector Hemingway in the eye, he was unable to keep a tremor out of his voice.

When Hemingway asked him if he had tried to open the door into his master’s room, he had to think for a moment before replying that he had just turned the handle.