The Naval Treaty

"The Naval Treaty", one of the 56 Sherlock Holmes short stories written by Sir Arthur Conan Doyle, is one of 12 stories in the cycle collected as The Memoirs of Sherlock Holmes. Doyle ranked "The Adventure of the Naval Treaty" 19th in a list of his 19 favourite Sherlock Holmes stories.
Dr. Watson receives a letter, which he then refers to Holmes, from an old schoolmate, now a Foreign Office employee from Woking who has had an important naval treaty stolen from his office. It disappeared while Mr. Percy Phelps had stepped out of his office momentarily late in the evening to see about some coffee that he had ordered. His office has two entrances, each joined by a stairway to a single landing. The commissionaire kept watch at the main entrance. There was no-one watching at the side entrance. Phelps also knew that his fiancée's brother was in town and that he might drop by. Phelps was alone in the office.