In his interview with Jabez Wilson, Holmes learns that Vincent Spaulding was the one who pointed out the advertisement for the Red-Headed League to Wilson, that Wilson is working at the Red-Headed League office every day from 10 A.M. until 2 P.M., that Spaulding is interested in photography and is always going down into Wilson's basement to develop films, that he offered to work for only half the usual wages, and that he has a certain distinctive mark on his face. Holmes makes a visit to the neighborhood of Wilson's pawnshop and stops by to ask Spaulding for directions. He observes that Spaulding has dirt on his trouser legs. Then he and Watson take a look around the immediate neighborhood and see that there is a branch of the City and Suburban Bank located close by. Holmes has recognized Spaulding as a notorious criminal named John Clay, and the detective deduces from what he has learned and observed that Clay is digging a tunnel from Wilson's basement to the basement of the bank. Holmes ascertains that the bank is storing a large shipment of gold coins.
Doyle modeled Holmes on a prominent physician who was a remarkable diagnostician. So Holmes could make a good doctor. He could also make a good lawyer because of his shrewd mind. He is naturallly interested in many branches of science, including chemistry, so he could make an excellent scientist--possibly a chemist or a naturalist like Charles Darwin. Holmes would also be a great police detective, a judge, or an investment broker.