The Adventure of the Second Stain

Background

The Prime Minister, Lord Bellinger, and the European Secretary, Trelawney Hope, ask Holmes to recover a document stolen from Hope's dispatch box at his home in Whitehall Terrace. It is an injudicious letter from a foreign potentate, and if it were made public it could bring war to Europe.

Holmes means to start with the spies he knows, but Watson tells him that one of them, Eduardo Lucas, has been murdered. Then Hope's wife, Lady Hilda Trelawney Hope, arrives unexpectedly at 221B Baker Street, presses Holmes about the document's contents, and begs him to tell her husband nothing of her visit.

Inspector Lestrade calls Holmes to the murder scene because the blood that soaked through the drugget left no stain on the floor beneath it, while there is a stain under the opposite edge. Holmes realises someone moved the carpet, finds an empty hiding place in the floor, and the constable on guard admits he let in a young woman, whom he recognises from a photograph Holmes shows him.

Confronted, Lady Hilda admits that Lucas was blackmailing her with a compromising letter she had written years earlier and demanded the document as payment. Holmes has it put back in the dispatch box with her duplicate key, lets Hope believe it was there all along, and answers the suspicious Prime Minister, "We also have our diplomatic secrets."