 After a civil servant at the Naval Patent Office is found with his head crushed adjacent to the open-air tracks of the London Underground, Holmes  brother Mycroft enlists Sherlock s help on the case The murdered man has apparently stolen top-secret plans for ten components of a new, state-of-the-art submarine, but only seven of the less important design plans are found on the body. Holmes and Watson are entrusted to find the three critically important missing blueprints.