In "The Red-Headed League," Mr. Wilson comes to Mr. Holmes for help, as he feels he has lost out on a very good job due to mysterious circumstances.
Mr. Wilson tells Holmes and Watson that he had recently seen an advertisement in the paper for a vacant position with something called The Red-Headed League. The advertisement said that all men over the age of twenty one, with red hair and good health, should apply in person the following Monday at the League's office on Fleet Street. When Mr. Wilson arrived to apply, he saw hundreds of other men with red hair lined up outside. Upon entry to the office, the man conducting interviews praised him as most suited for the job, and offered it to him on the spot.
Mr. Wilson already held a job as a pawnbroker but mostly conducted business in the evenings, and decided to take the mysterious job with The Red-Headed League, which promised he would only need to work from 10AM to 2PM. For the next weeks, Mr. Wilson was paid four pounds a week (quite a lot of money back then) to copy out the Encyclopedia Britannica by hand for a few hours a day.
Suddenly, on the 9th of October 1890, Mr. Wilson went to work and found a sign upon the office door reading, "The Red-Headed League is dissolved." Mr. Wilson checked with the landlord to ask about his employer, who said that the man had only rented the room and moved elsewhere in the city. When Wilson went to the new address, he found it to be a prosthetic knee manufacturer, and the people there had never heard of The Red-Headed League.
Wilson was both upset at losing such an easy, well-paying job and confused by its sudden disappearance. He has come to Sherlock Holmes to hire him to figure out where The Red-Headed League and/or the men who employed Wilson had gone. Holmes asks a few additional questions about Wilson's assistant, who he describes as handy and stout, with an acid scar on his face. After that, Holmes and Watson set off to begin investigating.
Source: The Works of Sir Arthur Conan Doyle: Complete and Unabridged (1983)