In 1878, Dr. Watson finishes his medical studies in London and trains as an army surgeon. He is sent to Afghanistan, where he is struck on the shoulder by a bullet that shattered the bone. Weak and injured, he returns to England alone, with no friends or family there.
In London, he stays in a private hotel. One day, he meets Stamford in a bar. They go for luncheon together in a hansom cab. As they rattled through the streets, Stamford looks at Watson and says, "You are as thin as a lath." Watson explains he is looking for cheap, comfortable rooms. Stamford says that another man is also looking for a roommate – and his name is Sherlock Holmes. Stamford describes him as a strange but decent fellow enough. Watson agrees to meet him.
They go to the laboratory, which is a lofty chamber full of bottles and tables. Holmes is busy with an experiment. He shows them a new test for blood. He explains that his re-agent is precipitated by hemoglobin and by nothing else. He named it an infallible test for blood stains. To demonstrate, he digs a long bodkin into his finger and adds a small quantity of blood to water. Then he adds some crystals and a liquid. The mixture changes colour instantly. Holmes is delighted and says this test will help catch criminals. He says that in many cases, his test will be decisive. Watson simply murmured his congratulations, surprised by Holmes's excitement.
Then Stamford reminds Holmes they came here on business – to talk about sharing rooms. Holmes knows a good place on Baker Street. He asks Watson if he minds tobacco smoke, chemical smells, or long silences. Watson says no. He mentions his own habits: he has a bull pup, hates noise, and he is lazy. He calls these his main vices. Holmes asks about violin-playing, and Watson says it depends on the player. They agree to see the rooms tomorrow.
The next day, they visit 221B Baker Street. The rooms are comfortable, and they move in. Holmes is quiet and regular in his habits. He spends time in the laboratory, in the dissecting-rooms, or on long walks. Sometimes he lies on the sofa without speaking for hours. Watson becomes more interested in him. But Watson is surprised to find that Holmes knows nothing about literature, philosophy, politics, or even the Solar System. Holmes explains that his brain is like an empty attic. He only keeps useful knowledge and forgets everything else. He says that knowing about the Sun or the Moon makes no difference to his work.
