Jabez Wilson's assistant, who calls himself Vincent Spaulding, and his partner in crime, who calls himself Duncan Ross, are digging a tunnel from the cellar under Wilson's pawnshop to the basement strongroom of a nearby bank for the purpose of stealing a large quantity of gold coins stored there. The bank director Mr. Merryweather, who comes to the strongroom late at night with Holmes and Watson and a policeman from Scotland Yard, explains exactly what it is the thieves are after.
We had occasion some months ago to strengthen our resources and borrowed for that purpose 30,000 napoleons from the Bank of France. It has become known that we have never had occasion to unpack the money, and that it is still lying in our cellar. The crate upon which I sit contains 2,000 napoleons packed between layers of lead foil.
These, of course, are gold coins stamped with the image of Napoleon Bonaparte. Their total value is thirty thousand English pounds, which was a large fortune in the days of Sherlock Holmes. Evidently there are fifteen crates, each containing two thousand coins. The thieves do not intend to drag the crates through their tunnel but will dump the coins into bags which would be easier to handle. Even so, it would take them many hours to get all the gold through the tunnel and into Jabez Wilson's cellar. They are planning to do the job on a Saturday night and make off with the loot in a hired wagon early Sunday morning while Wilson is asleep.
But Holmes has deduced what the two thieves are up to, and he is waiting for them with Watson, Merryweather, and Peter Jones, the official police agent, when Vincent Spaulding, who is really John Clay, "the murderer, thief, smasher, and forger," breaks through the flooring. The whole purpose of the Red-Headed League hoax was to get Jabez Wilson out of the way so that the two thieves could work on their tunnel together and make much faster progress.