Mr. Percy Phelps, a Foreign Office employee, is desperate. An important naval treaty disappeared while he was working with it during one late night in the office. Phelps reaches out to his old schoolmate, Holmes, and asks for his help. A long and exhausting investigation begins. But it is a matter of time for the treaty to be divulged to a foreign government. Will Holmes solve the case in time? Will Phelps win his good reputation back? "The Adventure of the Naval Treaty" is a part of "The Memoirs of Sherlock Holmes".