In the story, the body of a junior clerk named Cadogan West is found on the tracks outside Aldgate, with a number of stolen plans for the Bruce-Partington submarine in his pocket. It seems clear enough that "the man, dead or alive, either fell or was precipitated from a train." But why, wonders Holmes, did the dead man not have a ticket? It turns out that the body was placed on top of a train carriage "before" it reached Aldgate, via a window in a house on a cutting overlooking the Metropolitan line. Holmes realises that the body fell off the carriage roof only when the train was jolted by the dense concentration of points at Aldgate.