: An elderly professor falls in love with a young girl and leaves for London. Upon returning from the professor, strange attacks begin. Sherlock Holmes discovers that the cause of the attacks is an anti-aging drug.

Sherlock Holmes is being asked for help by a young man, Mr. Bennet, who is an assistant to the famous Professor Presbury and the groom of his only daughter.

Professor Presbury, a famous European scientist, in whose life science is in the first place, is a widower with an impeccable reputation. A few months ago, a professor who was sixty-one years old, with the fiery passion of a young man, made an offer to the daughter of his colleague. The girl liked him, but his age interfered. Around the same time, the professor left and did not tell anyone where. His family accidentally learned that he was in Prague.

Upon returning to the professor, strange things began to happen. He received letters marked with a cross from London, which Mr. Bennett, the personal secretary of the professor, was forbidden to open. Once, the professor was very angry when Mr. Bennett accidentally picked up the box that he brought from the trip. His dog began to pounce on the professor. The night before yesterday, Mr. Bennet heard some strange sounds.Looking out into the corridor, he saw a professor walking along the corridor on all fours, fully resting on his feet and hanging his head between his hands. Seeing this, Mr. Bennet asked if he needed help, but the professor growled something and ran away.

Together with Mr. Bennett, the bride comes to the detective and his daughter, the daughter of a professor, who says that she was woken up by a dog barking last night. Waking up, she looked out the window on the third floor and with horror saw her father's face in front of her. Dr. Watson, who is present here, is trying to determine what professors may have mental and physical illnesses. The whole point is that such strange things happen to him periodically, but he is still in his right mind and mind.

The great detective decides to visit the professor on the pretext of an appointment. However, the professor remembers very well that he did not make any appointments. Holmes inspects the house. The professor could reach the window of his daughter on the third floor only through ivy and a drainpipe, which is almost impossible for a normal person to do.

The great detective also finds out that the professor receives letters from London from a certain Czech Dorak. Paying attention to the dates of receipt of letters, Holmes notices that attacks of the professor happen every nine days. Most likely, he is taking some kind of remedy that was recommended to him in Prague.

As soon as the professor receives another letter from London, Mr. Bennet informs Holmes, and the great detective with Dr. Watson arrives at the professor's house.On the way, Holmes suddenly recalls that the professor’s finger joints are thicker and callosity.

In the evening, hiding, Holmes and Watson see how the professor leaves the house, gets on all fours and walks up to the ivy-covered wall. He nimbly climbs the wall, flying from branch to branch. Going down, he again gets on all fours and goes home, but then his dog, breaking the chain, rushes at him.

Having provided medical assistance to the professor, Holmes, Watson and Bennet open the box. There they find a letter stating that the professor was offered to use anti-aging serum. But it is not difficult for one who tries to put himself above Mother Nature to slide down.