‘No, it had fallen on the rug. (I’m afraid the acid’s ruined the rug, by the way.) I picked the glass up and put it back on the table.’

‘I’m glad you’ve told us that. There are only two sets of fingerprints on it, and one set is certainly Miss Johnson’s own. The other must be yours.’

He was silent for a moment, then he said: ‘Please go on.’

I described carefully what I’d done and the methods I had tried, looking rather anxiously at Dr Reilly for approval. He gave it with a nod.

‘You tried everything that could possibly have done any good,’ he said. And though I was pretty sure I had done so, it was a relief to have my belief confirmed.

‘Did you know exactly what she had taken?’ Captain Maitland asked.

‘No – but I could see, of course, that it was a corrosive acid.’

Captain Maitland asked gravely: ‘Is it your opinion, nurse, that Miss Johnson deliberately administered this stuff to herself?’

‘Oh, no,’ I exclaimed. ‘I never thought of such a thing!’

I don’t know why I was so sure. Partly, I think, because of M. Poirot’s hints. His ‘murder is a habit’ had impressed itself on my mind. And then one doesn’t readily believe that anyone’s going to commit suicide in such a terribly painful way.

I said as much and Captain Maitland nodded thoughtfully. ‘I agree that it isn’t what one would choose,’ he said. ‘But if anyone were in great distress of mind and this stuff were easily obtainable it might be taken for that reason.’

‘Was she in great distress of mind?’ I asked doubtfully.

‘Mrs Mercado says so. She says that Miss Johnson was quite unlike herself at dinner last night – that she hardly replied to anything that was said to her. Mrs Mercado is quite sure that Miss Johnson was in terrible distress over something and that the idea of making away with herself had already occurred to her.’

‘Well, I don’t believe it for a moment,’ I said bluntly.

Mrs Mercado indeed! Nasty slinking little cat!

‘Then what do you think?’

‘I think she was murdered,’ I said bluntly.

He rapped out his next question sharply. I felt rather that I was in the orderly room.

‘Any reasons?’

‘It seems to me by far and away the most possible solution.’

‘That’s just your private opinion. There was no reason why the lady should be murdered?’

‘Excuse me,’ I said, ‘there was. She found out something.’

‘Found out something? What did she find out?’

I repeated our conversation on the roof word for word.

‘She refused to tell you what her discovery was?’

‘Yes. She said she must have time to think it over.’

‘But she was very excited by it?’

‘Yes.’

‘A way of getting in from outside.’ Captain Maitland puzzled over it, his brows knit. ‘Had you no idea at all of what she was driving at?’

‘Not in the least. I puzzled and puzzled over it but I couldn’t even get a glimmering.’

Captain Maitland said: ‘What do you think, M. Poirot?’

Poirot said: ‘I think you have there a possible motive.’

‘For murder?’

‘For murder.’

Captain Maitland frowned.

‘She wasn’t able to speak before she died?’

‘Yes, she just managed to get out two words.’

‘What were they?’

‘The window…’

‘The window?’ repeated Captain Maitland. ‘Did you understand to what she was referring?’

I shook my head.

‘How many windows were there in her bedroom?’

‘Just the one.’

‘Giving on the courtyard?’

‘Yes.’

‘Was it open or shut? Open, I seem to remember. But perhaps one of you opened it?’

‘No, it was open all the time. I wondered–’

I stopped.

‘Go on, nurse.’

‘I examined the window, of course, but I couldn’t see anything unusual about it. I wondered whether, perhaps, somebody changed the glasses that way.’

‘Changed the glasses?’

‘Yes. You see, Miss Johnson always takes a glass of water to bed with her. I think that glass must have been tampered with and a glass of acid put in its place.’

‘What do you say, Reilly?’

‘If it’s murder, that was probably the way it was done,’ said Dr Reilly promptly. ‘No ordinary moderately observant human being would drink a glass of acid in mistake for one of water – if they were in full possession of their waking faculties. But if anyone’s accustomed to drinking off a glass of water in the middle of the night, that person might easily stretch out an arm, find the glass in the accustomed place, and still half asleep, toss off enough of the stuff to be fatal before realizing what had happened.’

Captain Maitland reflected a minute.

‘I’ll have to go back and look at that window. How far is it from the head of the bed?’

I thought.

‘With a very long stretch you could just reach the little table that stands by the head of the bed.’

‘The table on which the glass of water was?’

‘Yes.’

‘Was the door locked?’

‘No.’

‘So whoever it was could have come in that way and made the substitution?’

‘Oh, yes.’

‘There would be more risk that way,’ said Dr Reilly. ‘A person who is sleeping quite soundly will often wake up at the sound of a footfall. If the table could be reached from the window it would be the safer way.’

‘I’m not only thinking of the glass,’ said Captain Maitland absent-mindedly.

Rousing himself, he addressed me once again.

‘It’s your opinion that when the poor lady felt she was dying she was anxious to let you know that somebody had substituted acid for water through the open window? Surely the person’s name would have been more to the point?’

‘She mayn’t have known the name,’ I pointed out.

‘Or it would have been more to the point if she’d managed to hint what it was that she had discovered the day before?’

Dr Reilly said: ‘When you’re dying, Maitland, you haven’t always got a sense of proportion. One particular fact very likely obsesses your mind. That a murderous hand had come through the window may have been the principal fact obsessing her at the minute. It may have seemed to her important that she should let people know that. In my opinion she wasn’t far wrong either. It was important! She probably jumped to the fact that you’d think it was suicide. If she could have used her tongue freely, she’d probably have said “It wasn’t suicide. I didn’t take it myself. Somebody else must have put it near my bedthrough the window.”’

Captain Maitland drummed with his fingers for a minute or two without replying. Then he said:

‘There are certainly two ways of looking at it. It’s either suicide or murder. Which do you think, Dr Leidner?’

Dr Leidner was silent for a minute or two, then he said quietly and decisively: ‘Murder. Anne Johnson wasn’t the sort of woman to kill herself.’

‘No,’ allowed Captain Maitland. ‘Not in the normal run of things. But there might be circumstances in which it would be quite a natural thing to do.’

‘Such as?’

Captain Maitland stooped to a bundle which I had previously noticed him place by the side of his chair. He swung it on to the table with something of an effort.

‘There’s something here that none of you know about,’ he said. ‘We found it under her bed.’

He fumbled with the knot of the covering, then threw it back, revealing a heavy great quern or grinder.

That was nothing in itself – there were a dozen or so already found in the course of the excavations.

What riveted our attention on this particular specimen was a dull, dark stain and a fragment of something that looked like hair.

‘That’ll be your job, Reilly,’ said Captain Maitland. ‘But I shouldn’t say that there’s much doubt about this being the instrument with which Mrs Leidner was killed!’