To make things clear and explain the position, I have appended a rough sketch of the right-hand wing of the house. The small staircase leads, as Parker explained, to a big bedroom made by two being knocked into one, and an adjoining bathroom and lavatory.

The inspector took in the position at a glance. We went through into the large hall and he locked the door behind him, slipping the key into his pocket. Then he gave the constable some low-voiced instructions, and the latter prepared to depart.

‘We must get busy on those shoe tracks,’ explained the inspector. ‘But first of all, I must have a word with Miss Ackroyd. She was the last person to see her uncle alive. Does she know yet?’

Raymond shook his head.

‘Well, no need to tell her for another five minutes. She can answer my questions better without being upset by knowing the truth about her uncle. Tell her there’s been a burglary, and ask her if she would mind dressing and coming down to answer a few questions.’

It was Raymond who went upstairs on this errand.

‘Miss Ackroyd will be down in a minute,’ he said, when he returned. ‘I told her just what you suggested.’

In less than five minutes Flora descended the staircase. She was wrapped in a pale pink silk kimono. She looked anxious and excited.

The inspector stepped forward.

‘Good evening, Miss Ackroyd,’ he said civilly. ‘We’re afraid there’s been an attempt at robbery, and we want you to help us. What’s this room – the billiard room? Come in here and sit down.’

Flora sat down composedly on the wide divan which ran the length of the wall, and looked up at the inspector.

‘I don’t quite understand. What has been stolen? What do you want me to tell you?’

‘It’s just this, Miss Ackroyd. Parker here says you came out of your uncle’s study at about a quarter to ten. Is that right?’

‘Quite right. I had been to say goodnight to him.’

‘And the time is correct?’

‘Well, it must have been about then. I can’t say exactly. It might have been later.’

‘Was your uncle alone, or was there anyone with him?’

‘He was alone. Dr Sheppard had gone.’

‘Did you happen to notice whether the window was open or shut?’

Flora shook her head.

‘I can’t say. The curtains were drawn.’

‘Exactly. And your uncle seemed quite as usual?’

‘I think so.’

‘Do you mind telling us exactly what passed between you?’

Flora paused a minute, as though to collect her recollections.

‘I went in and said, ‘goodnight, uncle, I’m going to bed now. I’m tired tonight.’ he gave a sort of grunt, and – I went over and kissed him, and he said something about my looking nice in the frock I had on, and then he told me to run away as he was busy. So I went.’

‘Did he ask specially not to be disturbed?’

‘Oh! yes, I forgot. He said: “Tell Parker I don’t want anything more tonight, and that he’s not to disturb me.” I met Parker just outside the door and gave him uncle’s message.’

‘Just so,’ said the inspector.

‘Won’t you tell me what it is that has been stolen?’

‘We’re not quite – certain,’ said the inspector hesitatingly.

A wide look of alarm came into the girl’s eyes. She started up.

‘What is it? You’re hiding something from me?’

Moving in his usual unobtrusive manner, hector Blunt came between her and the inspector. She half stretched out her hand, and he took it in both of his, patting it as though she were a very small child, and she turned to him as though something in his stolid, rocklike demeanour promised comfort and safety.

‘It’s bad news, Flora,’ he said quietly. ‘Bad news for all of us. Your uncle Roger – ’

‘Yes?’

‘It will be a shock to you. Bound to be. Poor roger’s dead.’

Flora drew away from him, her eyes dilating with horror.

‘When?’ she whispered. ‘When?’

‘Very soon after you left him, I’m afraid,’ said Blunt gravely.

Flora raised her hand to her throat, gave a little cry, and I hurried to catch her as she fell. She had fainted, and Blunt and I carried her upstairs and laid her on her bed. Then I got him to wake Mrs Ackroyd and tell her the news. Flora soon revived, and I brought her mother to her, telling her what to do for the girl. Then I hurried downstairs again.

I met the inspector just coming from the door which led into the kitchen quarters.

‘How’s the young lady, doctor?’

‘Coming round nicely. Her mother’s with her.’

‘That’s good. I’ve been questioning the servants. They all declare that no one has been to the back door tonight. Your description of that stranger was rather vague. Can’t you give us something more definite to go upon?’

‘I’m afraid not,’ I said regretfully. ‘It was a dark night, you see, and the fellow had his coat collar well pulled up and his hat squashed down over his eyes.’

‘H’m,’ said the inspector. ‘Looked as though he wanted to conceal his face. Sure it was no one you know?’

I replied in the negative, but not as decidedly as I might have done. I remembered my impression that the stranger’s voice was not unfamiliar to me. I explained this rather haltingly to the inspector.

‘It was a rough, uneducated voice, you say?’

I agreed, but it occurred to me that the roughness had been of an almost exaggerated quality. If, as the inspector thought, the man had wished to hide his face, he might equally well have tried to disguise his voice.

‘Do you mind coming into the study with me again, doctor? There are one or two things I want to ask you.’

I acquiesced. Inspector Davis unlocked the door of the lobby, we passed through, and he locked the door again behind him.

‘We don’t want to be disturbed,’ he said grimly. ‘And we don’t want any eavesdropping either. What’s all this about blackmail?’

‘Blackmail!’ I exclaimed, very much startled.

‘Is it an effort of Parker’s imagination? Or is there something in it?’

‘If Parker heard anything about blackmail,’ I said slowly, ‘he must have been listening outside this door with his ear glued against the keyhole.’

Davis nodded.

‘Nothing more likely. You see, I’ve been instituting a few inquiries as to what Parker has been doing with himself this evening. To tell the truth, I didn’t like his manner. The man knows something. When I began to question him, he got the wind up, and plumped out some garbled story of blackmail.’

I took an instant decision.

‘I’m rather glad you’ve brought the matter up,’ I said. ‘I’ve been trying to decide whether to make a clean breast of things or not. I’d already practically decided to tell you everything, but I was going to wait for a favourable opportunity. You might as well have it now.’

And then and there I narrated the whole events of the evening as I have set them down here. The inspector listened keenly, occasionally interjecting a question.

‘Most extraordinary story I ever heard,’ he said, when I had finished. ‘And you say that letter has completely disappeared? It looks bad – it looks very bad indeed. It gives us what we’ve been looking for – a motive for the murder.’

I nodded. ‘I realize that.’

‘You say that Mr Ackroyd hinted at a suspicion he had that some member of his household was involved? household’s rather an elastic term.’