In the story, a senior British politician receives a strongly worded letter from a European king which criticizes British foreign policy. If the contents of the letter were made public, the reaction of the British people would make war inevitable. When the letter is stolen, the Prime Minister calls on the brilliant consulting detective Sherlock Holmes for assistance. The case is further complicated when Holmes discovers that a foreign spy whom he suspects of stealing the letter was murdered at around the same time that the letter was stolen.