In Arthur Conan Doyle’s “The Adventure of the Naval Treaty,” what is the missing document about?

In Arthur Conan Doyle’s “The Adventure of the Naval Treaty,” the missing document is a secret naval treaty.

The story concerns Percy Phelps, a young Foreign Office employee who is entrusted with copying an important diplomatic document. While working late, Phelps discovers that the treaty has disappeared from his office. The loss threatens Britain’s international position and causes a severe personal crisis for him.

Dr Watson receives Phelps’s account and takes Holmes to investigate. Holmes studies the physical circumstances of the disappearance rather than accepting the first apparent explanation. The case ultimately turns on the document’s value and the practical opportunities available to whoever removed it.

The story was first published in 1893 and later included in The Memoirs of Sherlock Holmes. Its title refers to the diplomatic document itself, not to a naval battle or a ship.