In "The Red-headed League," when Dr. Watson meets Mr. Holmes later in the evening he is introduced to two other men who will be accompanying them...

The two men are a police officer and the bank director and Holmes wants them to witness the bank robbery attempt.

When Holmes is visited by a client who claims that he was employed by a strange organization that suddenly vanished, it seems like an interesting case. Holmes realizes that the mystery is not about the “Red-headed League,” which does not exist.  The League is a cover-up for something much more sinister—a bank robbery.

Mr....

The two men are a police officer and the bank director and Holmes wants them to witness the bank robbery attempt.

When Holmes is visited by a client who claims that he was employed by a strange organization that suddenly vanished, it seems like an interesting case. Holmes realizes that the mystery is not about the “Red-headed League,” which does not exist.  The League is a cover-up for something much more sinister—a bank robbery.

Mr. Wilson is a shopkeeper.  His assistant is the one who suggested he apply for the League position.  Holmes visited the shop and talked to the assistant, and realized that the man was spending a lot of time in the basement and the League was invented to get Mr. Wilson out of the shop so that he could have access to the bank next door.

Holmes does not stop them.  Instead, he wants to catch them in the act.  

On entering his room, I found Holmes in animated conversation with two men, one of whom I recognized as Peter Jones, the official police agent; while the other was a long, thin, sad-faced man, with a very shiny hat and oppressively respectable frock coat.

The second man is the bank director, Merryweather.  They all hide in the basement of the City and Suburban Bank and wait for John Clay to rob it that night.  They are not disappointed.

Sherlock Holmes had sprung out and seized the intruder by the collar. The other dived down the hole, and I heard the sound of rending cloth as Jones clutched at his skirts. 

The criminals were caught in the act, and the mystery of The Red-headed League was solved.  John Clay got himself a job as the assistant to Mr. Wilson to rob the bank.  Holmes recognized him by the description and knew that he was a very intelligent, ruthless, and creative criminal.  He was sure he had some big plans for getting Mr. Wilson out of the shop.