“The practical application of what I have said is very close to the problem which I am investigating. It is a tangled skein, you understand, and I am looking for a loose end. One possible loose end lies in the question: Why does Professor Presbury’s wolfhound, Roy, endeavour to bite him?”

I sank back in my chair in some disappointment. Was it for so trivial a question as this that I had been summoned from my work? Holmes glanced across at me.

“The same old Watson!” said he. “You never learn that the gravest issues may depend upon the smallest things. But is it not on the face of it strange that a staid, elderly philosopher - you’ve heard of Presbury, of course, the famous Camford physiologist? - that such a man, whose friend has been his devoted wolfhound, should now have been twice attacked by his own dog? What do you make of it?”

“The dog is ill.”

“Well, that has to be considered. But he attacks no one else, nor does he apparently molest his master, save on very special occasions. Curious, Watson - very curious. But young Mr. Bennett is before his time if that is his ring. I had hoped to have a longer chat with you before he came.”

There was a quick step on the stairs, a sharp tap at the door, and a moment later the new client presented himself. He was a tall, handsome youth about thirty, well dressed and elegant, but with something in his bearing which suggested the shyness of the student rather than the self-possession of the man of the world. He shook hands with Holmes, and then looked with some surprise at me.

“This matter is very delicate, Mr. Holmes,” he said. “Consider the relation in which I stand to Professor Presbury both privately and publicly. I really can hardly justify myself if I speak before any third person.”

“Have no fear, Mr. Bennett. Dr. Watson is the very soul of discretion, and I can assure you that this is a matter in which I am very likely to need an assistant.”

“As you like, Mr. Holmes. You will, I am sure, understand my having some reserves in the matter.”

“You will appreciate it, Watson, when I tell you that this gentleman, Mr. Trevor Bennett, is professional assistant to the great scientist, lives under his roof, and is engaged to his only daughter. Certainly we must agree that the professor has every claim upon his loyalty and devotion. But it may best be shown by taking the necessary steps to clear up this strange mystery.”

“I hope so, Mr. Holmes. That is my one object. Does Dr. Watson know the situation?”

“I have not had time to explain it.”

“Then perhaps I had better go over the ground again before explaining some fresh developments.”

“I will do so myself,” said Holmes, “in order to show that I have the events in their due order. The professor, Watson, is a man of European reputation. His life has been academic. There has never been a breath of scandal. He is a widower with one daughter, Edith. He is, I gather, a man of very virile and positive, one might almost say combative, character. So the matter stood until a very few months ago.

“Then the current of his life was broken. He is sixty-one years of age, but he became engaged to the daughter of Professor Morphy, his colleague in the chair of comparative anatomy. It was not, as I understand, the reasoned courting of an elderly man but rather the passionate frenzy of youth, for no one could have shown himself a more devoted lover. The lady, Alice Morphy, was a very perfect girl both in mind and body, so that there was every excuse for the professor’s infatuation. None the less, it did not meet with full approval in his own family.”

“We thought it rather excessive,” said our visitor.