Sir Henry's business trip. This time he decided to go to Tangier, to take a break from mysteries and locked rooms. However, it is not meant to be. Police Chief Duroc turns to G.M. for help in catching the elusive burglar known as the Iron Chest. This virtuoso has already visited almost all the capitals of the Old World and robbed a bank or jewelry store in each of them, dissolving into thin air after the crime. And according to all data, the next target of the Iron Chest will be the Sultan’s diamonds in Tangier. Having broken down for the sake of decency, Sir Henry, of course, agrees to help.