Junior clerk at the Arsenal office, Arthur Cadogan West, is found murdered on the tube tracks. Plans for the Bruce-Partington submarine, which had been kept in a secure safe in the Secret Department - in a room adjacent to the Arsenal - were found in West's pocket. He had seven plans on him, but three of the most important ones were missing...

Late in the evening, a young hydraulic engineer named Victor Hederly arrived at Iford Station at the request of Colonel Stark. Stark needed his opinion on a hydraulic press that had broken down. Arriving with the colonel, the hydraulic engineer examined the press and determined the cause of the malfunction, but then he rashly began to examine the metal floor of the press and found himself locked inside the structure with the mechanism on...