Who was trying to rob the bank?
A notorious criminal named John Clay is plotting to loot the Coburg branch of the City and Suburban Bank's underground strongroom of 30,000 French gold coins worth 30,000 British pounds. Just before the climax of the story, Mr. Jones, the Scotland Yard detective, describes their quarry as follows:
“John Clay, the murderer, thief, smasher, and forger. He's a young man, Mr. Merryweather, but he is at the head of his profession, and I would rather have my bracelets on him than on any criminal in London. He's a remarkable man, is young John Clay. His grandfather was a royal duke, and he himself has been to Eton and Oxford. His brain is as cunning as his fingers, and though we meet signs of him at every turn, we never know where to find the man himself. He'll crack a crib in Scotland one week, and be raising money to build an orphanage in Cornwall the next. I've been on his track for years and have never set eyes on him yet.”
Clay has an accomplice who calls himself Duncan Ross when he pretends to be in charge of the offices of the Red-Headed League. Evidently his first name is Archie, because that is what Clay calls him when he realizes that the jig is up.
“It's all clear,” he whispered. “Have you the chisel and the bags? Great Scott! Jump, Archie, jump, and I'll swing for it!”
Clay has gotten a job with the pawnbroker Jabez Wilson in order to be able to dig a tunnel from Wilson's cellar to the bank. Clay is using the name Vincent Spaulding. When Wilson goes to Sherlock Holmes, he describes his new assistant as follows:
“Small, stout-built, very quick in his ways, no hair on his face, though he's not short of thirty. Has a white splash of acid upon his forehead.”
Vincent Spaulding pretends to be very interested in photography. This is to explain to Wilson why he is always going down into the cellar. He is supposedly developing photographs in the dark, but he is really working on the tunnel every chance he can get. After he and his accomplice have gotten Jabez Wilson out of the way for four hours each day plus the time it takes to get to and from the office, they can work on the tunnel together. Time is of the essence. There is a strong likelihood that all that gold will soon be moved elsewhere.
What has brought Jabez Wilson to Sherlock Holmes' flat on Baker Street is that he has just received notice that the Red-Headed League has been dissolved as of that day. Holmes deduces that the thieves must have completed their tunnel and are planning to loot the bank that night. They had invented the Red-Headed League to get Wilson out of the way for four or five hours every day but Sunday while they worked feverishly on their long tunnel. Now that they were ready to break through the flooring of the bank strongroom, they no longer needed Wilson's absence, so they dissolved the phony League.