“Absolutely!” said I. “And now that you have explained it, I confess that I am as amazed as before.”

“It was very superficial, my dear Watson, I assure you. I should not have intruded it upon your attention had you not shown some incredulity the other day. But the evening has brought a breeze with it. What do you say to a ramble through London?”

I was weary of our little sitting-room and gladly acquiesced. For three hours we strolled about together, watching the everchanging kaleidoscope of life as it ebbs and flows through Fleet Street and the Strand. His characteristic talk, with its keen observance of detail and subtle power of inference, held me amused and enthralled. It was ten o’clock before we reached Baker Street again. A brougham was waiting at our door.

“Hum! A doctor’s — general practitioner, I perceive,” said Holmes. “Not been long in practice, but has a good deal to do. Come to consult us, I fancy! Lucky we came back!”

I was sufficiently conversant with Holmes’s methods to be able to follow his reasoning, and to see that the nature and state of the various medical instruments in the wicker basket which hung in the lamp-light inside the brougham had given him the data for his swift deduction. The light in our window above showed that this late visit was indeed intended for us. With some curiosity as to what could have sent a brother medico to us at such an hour, I followed Holmes into our sanctum.

A pale, taper-faced man with sandy whiskers rose up from a chair by the fire as we entered. His age may not have been more than three or four and thirty, but his haggard expression and unhealthy hue told of a life which had sapped his strength and robbed him of his youth. His manner was nervous and shy, like that of a sensitive gentleman, and the thin white hand which he laid on the mantelpiece as he rose was that of an artist rather than of a surgeon. His dress was quiet and sombre — a black frockcoat, dark trousers, and a touch of colour about his necktie.

“Good-evening, Doctor,” said Holmes cheerily. “I am glad to see that you have only been waiting a very few minutes.”

“You spoke to my coachman, then?”

“No, it was the candle on the side-table that told me. Pray resume your seat and let me know how I can serve you.”

“My name is Dr. Percy Trevelyan,” said our visitor, “and I live at 403 Brook Street.”

“Are you not the author of a monograph upon obscure nervous lesions?” I asked.

His pale cheeks flushed with pleasure at hearing that his work was known to me.

“I so seldom hear of the work that I thought it was quite dead,” said he. “My publishers gave me a most discouraging account of its sale. You are yourself, I presume, a medical man.”

“A retired army surgeon.”

“My own hobby has always been nervous disease. I should wish to make it an absolute specialty, but of course a man must take what he can get at first. This, however, is beside the question, Mr. Sherlock Holmes, and I quite appreciate how valuable your time is. The fact is that a very singular train of events has occurred recently at my house in Brook Street, and to-night they came to such a head that I felt it was quite impossible for me to wait another hour before asking for your advice and assistance.”