Watson has gone to Baker Street to meet Holmes. He goes into Holmes's apartment and notices that he is joined by two other men. The man seems a little bit skeptical about the whole thing. A wild goose chase is a sort of complicated case where you go from one thing to the other, and then ultimately you get nothing at the end of it. So maybe this tall man is somehow involved in in the crime. If he loses 30,000 pounds, maybe this John Clay, this Vincent Spalding, may be trying to steal money from this man. We'll see.