The Adventure of the Bruce-Partington Plans

It is one of eight stories in the cycle collected as His Last Bow, and is the second and final appearance of Mycroft Holmes. Holmes's brother Mycroft has come about some missing, secret submarine plans. The three missing pages of the plans could enable one of England's enemies to build the submarine and use it against her. It is up to the great detective to solve the murder and retrieve the missing plans and ensure England's future defense.