Holmes says that he first developed his methods of deduction as an undergraduate; his earliest cases, which he pursued as an amateur, came from fellow university students.[6] A meeting with a classmate's father led him to adopt detection as a profession,[7] and he spent six years after university as a consultant before financial difficulties led him to accept John H. Watson as a fellow lodger (when the narrative of the stories begins).
Beginning in 1881 Holmes has lodgings at 221B Baker Street, London. According to an early story[8] 221B is an apartment at the upper end of the street, up 17 steps. Until Watson's arrival Holmes worked alone, only occasionally employing agents from the city's underclass; these agents included a host of informants, and a group of street children he called "the Baker Street Irregulars". The Irregulars appear in three stories: A Study in Scarlet, The Sign of the Four and "The Adventure of the Crooked Man".
His parents are not mentioned in the stories, although Holmes mentions that his ancestors were "country squires". In "The Adventure of the Greek Interpreter", he claims that his great-uncle was French artist Horace Vernet. Holmes's brother Mycroft, seven years his senior, is a government official who appears in "The Adventure of the Greek Interpreter", "The Final Problem" and "The Adventure of the Bruce-Partington Plans" and is mentioned in "The Adventure of the Empty House". Mycroft has a unique civil service position as a kind of human database for all aspects of government policy. He lacks Sherlock's interest in physical investigation, however, preferring to spend his time at the Diogenes Club.