The monotony of thick smog-shrouded London is broken by a sudden visit from Holmes' brother Mycroft. He has come about some missing, secret submarine plans. Seven of the ten pages three are still missing were found with Arthur Cadogan West's body. He was a young clerk in a government office at Royal Arsenal, Woolwich, whose body was found next to the Underground tracks near the Aldgate tube station, his head crushed. He had little money with him, theatre tickets, and curiously, no Underground ticket. The three missing pages by themselves could enable one of Britain's enemies to build a Bruce-Partington submarine."Underground"-branded Tube map from 1908 showing the District and Metropolitan lines with Aldgate at right and Kensington at lower left It seems clear that Cadogan West fell from a train and that he stole the plans, meaning to sell them, but the mystery is truly complex.Inspector Lestrade tells Holmes that a passenger has seen fit to report hearing a thud at about the location in question, as though a body had fallen on the track. He could not see anything, however, owing to the thick fog. After an examination of the track near Aldgate, Holmes reaches an astonishing and unusual conclusion: West had been killed elsewhere, was deposited on the roof of an Underground train, and fell off when the jarring action of going across a railway point at Aldgate shook the coach.