Lord Bellinger, the Prime Minister, and the Right Honourable Trelawney Hope, the Secretary of State for European Affairs, come to Holmes in the matter of a document stolen from Hope's dispatch box, which he kept at home in Whitehall Terrace when not at work. If divulged, this document could bring about very dire consequences for all of Europe, even war. They are loath to tell Holmes at first the exact nature of the document's contents, but when Holmes declines to take on their case, they tell him it was a rather injudicious letter from a foreign potentate. It disappeared from the dispatch box one evening when Hope's wife was out at the theatre for four hours. No one in the house knew about the document, not even the Secretary's wife. None of the servants could have guessed what was in the box.

Holmes decides to begin with some spies known to him and is then astonished to hear from Dr. Watson that one of those that he names, Eduardo Lucas, has been murdered. Before Holmes has a chance to act, Lady Hilda Trelawney Hope, the European Secretary's wife, arrives unexpectedly at 221B Baker Street. She asks Holmes insistently about the stolen document's contents, but Holmes only reveals there would be regrettable consequences if the document were not found. Lady Hilda also begs Holmes to tell her husband nothing of her visit.