“Ah, yes!” said Holmes. “Edith Trubshaw! I remember the case well! As I recall, I was able to sort the matter out to her satisfaction.”

“So Mrs Walsh said. As soon as I remembered that, I at once wondered if you could perhaps sort my troubles out, too. There and then, I resolved to consult you as soon as possible. At the university archaeology department I met Mr Martin and mentioned my idea to him. To be honest, he was a bit dubious at first; he was unsure what you would be able to achieve, but as we discussed it, he became more enthusiastic. ‘If Mr Holmes could somehow discover what it is that lies behind all this,’ said he, ‘and what the secret is that Professor Palfreyman is keeping to himself, then perhaps it would be better for everyone. On the other hand,’ he added, ‘if the professor wants to keep his own secrets, that is his right, and we can hardly go prying into his private affairs. It cannot be denied that he sometimes seems rather delicately balanced, and we would not want our interference to make him worse.’

“‘No, of course not. But I shall put the matter in the hands of Mr Sherlock Holmes first thing tomorrow morning and see what he has to say about it. It will be a great relief to me to know that someone else is discreetly looking into the matter.’

“‘I agree,’ said Tim. ‘Do you know, Georgina, I think I shall call in at Bluebell Cottage later tomorrow, so you can tell me all about it!’

“I had several jobs to do in town before I could catch the train back to Beckenham. After my experience the previous week, I wanted to make sure this time that I didn’t leave it too late, so that it would still be light by the time I reached my destination. Unfortunately, however, I just missed the train I had intended to catch, and the one I did get was held up for nearly half an hour at Herne Hill, and then stuck in Penge tunnel for a further twenty minutes, so that by the time I reached Beckenham the light had gone completely. I considered taking a cab, but there were none there, so I set out to walk home as usual. This time, at least, I thought, I was mentally prepared and should not be so nervous on the quiet lanes to Bluebell Cottage. By the time I turned off the main road, however, there was absolutely no one about, and nothing to be heard but the drip, drip, drip among the trees on either side. The trees themselves, even those nearest to the lane, were but dark, shadowy shapes to me, and I began to wish I had waited for a cab after all. Forcing myself to look straight ahead and ignore the shifting fog among the trees, I pressed on. It was extremely cold and my cheeks felt as if they were touched by icy fingers.

“Then, when I knew I must be approaching Stagg’s Lane – although so thick was the fog that even the familiar little roadside landmarks were quite hidden from me – I heard, above the constant dripping of the trees, what sounded like someone moving through the wood to the left of the lane. I increased my speed slightly, but the movement at the side seemed to stay with me, then, out of the corner of my eye, I thought I saw a shadowy shape slip from one tree to the next. Without turning my head to the side, I picked up my skirts and broke into a run, breathing heavily. On down that lonely, muddy lane I ran, madly, frantically, as if running for my life. For an instant, I had the impression of something in the air to my left, then something struck me hard on the side of the head, and with a scream I tumbled forward into the mud.

“What happened next, I don’t know. As I tried to push myself up from the muddy ground, I heard muffled footsteps rapidly approaching. I think I may have screamed again, and then I passed out.

“When I came to, I was lying on the couch in the sitting room at Bluebell Cottage, with a fire blazing in the grate and a plaid blanket laid over me. Professor Palfreyman and Mrs Wheeler were standing there, speaking quietly, and they turned to me as I opened my eyes.

“‘There, there,’ said Mrs Wheeler. ‘How are you, my dear?’

“‘I feel a bit sick,’ I said. ‘What happened?’

“‘You’ve had a fall, my dear. Professor Palfreyman found you lying in the lane, in the mud, and carried you in. Here,’ she continued, picking up a cup and saucer from a side table, ‘have a sip of this. It’ll make you feel better!’

“‘Would you like something stronger?’ the professor asked as I sipped the tea, but I shook my head.

“‘I shall be all right in a minute,’ I said. I sat up, swung my feet to the floor and tried to stand up, but I staggered slightly and nearly fell over.

“‘Don’t try to stand,’ said the professor, rearranging the rug over my knees. ‘We must keep you warm,’ he added, pushing the couch a little nearer to the fire.

“‘What has happened to me?’ I repeated, feeling a little dizzy.

“‘I don’t know,’ said the professor, shaking his head. ‘Luckily, I happened to be out in the garden, and heard you cry out. You had fallen just near the corner of the lane. Did you trip?’

“‘No,’ I said. ‘Something struck me on the side of the head.’

“The professor leaned over and examined the side of my head. ‘There is a muddy mark there,’ said he, ‘but the skin is not broken. I wonder what it could have been?’

“‘I believe there was someone out there,’ I said, ‘who flung something at me. If it hasn’t cut me, then perhaps it was not a stone but a bit of stick. It certainly hurt, anyway.’

“‘How dreadful!’ said Mrs Wheeler.

“The professor shook his head in puzzlement. ‘It will be too dark out there to see anything now, but I’ll have a look first thing in the morning and see if I can find anything.’

“Later, Mrs Wheeler recommended a hot bath as being the best cure for a fall, as she referred to it, so I followed her suggestion. Afterwards I came downstairs in my dressing gown and sat for some time in the kitchen, watching her prepare some buttered toast and cocoa for me.

“‘What was Professor Palfreyman doing out in the garden in the dark?’ I asked her.

“She hesitated for a moment. ‘It was because of you, miss,’ she replied at length. ‘He didn’t want me to tell you, but he’s been worried about you all week. He came in the kitchen earlier, saying, “Isn’t that girl back yet?” and when I said, “No,” he said, “I’m worried about her, Mrs Wheeler. I think I’ll go out, walk up the lane a bit and see if I meet her!” The next thing I knew, he was coming in at the front door, carrying you in his arms and telling me to put the kettle on.’

“I retired to bed early last night, as you will imagine. Perhaps because of that, I woke in the middle of the night. I lit my candle and saw that it was half past three. As I did so, I heard the professor’s voice from the room next door. ‘No!’ he cried, ‘I don’t know!’ Then something about ‘danger!’ Then, after a long silence, ‘Don’t look at it!’ This was followed by a dull thud, and I guessed that he had knocked something over, or even fallen out of bed again. But this time, I stayed where I was. I felt too worn out and shaken up myself to minister to him. After a time, all was silent, and eventually I fell asleep once more. This morning I felt for the first time that I could no longer go on in this way, so as soon as we had had breakfast, I put my coat on and came away. There you are, Mr Holmes. Now you know everything, and here I am!”

Sherlock Holmes opened his eyes, but did not respond at once. Instead, he stared into the fire for some time, as if he might see a solution to this strange mystery in the flickering flames.

“Do you know,” he asked Miss Calloway at length, “if Professor Palfreyman has made any enquiries into where these strange, anonymous letters might have come from?”

“I don’t believe so,” she replied. “If he has, he has said nothing about it to me and, as I mentioned, he threw them both in the fire almost as soon as he had received them.”

“And the tile with the smiling face on it?”