Under the assumed name of Stapleton, Roger of Baskerville is condemned to death for being instrumental in the death of a relative and probable heir to the Baskerville estates. After his plea of clemency is denied, he overpowers his keeper and escapes, taking up his residence near Baskerville Castle, and announcing himself to Lord and Lady Baskerville as Loris Collamore, a new neighbor. The next day he succeeds in inveigling them into a submersible house which he has built in a nearby lake, and making them prisoners. He then goes to the castle and announces to the servants that he is a relative of Lord Henry and has come to take charge of his affairs. The servants become suspicious of the intruder, and being mystified at the strange disappearance of their master and mistress, seek the aid of Sherlock Holmes, who had been mainly instrumental in securing the conviction of Roger. The great detective takes up the case and in the course of his investigations is locked in a secret closet in the castle by the criminal, who has recognized him. Armed with a pocket wireless outfit. Holmes calls an assistant and is quickly released. Later, Holmes and his assistant see the submersible house and manage to get inside, where they learn that the Baskervilles are prisoners. When Roger sees that his nefarious scheme has been frustrated he breaks the windows, thus allowing the water to enter, but in the struggle which follows Holmes reaches the raising mechanism and. the house slowly rises out of the lake. The prisoners are freed and Roger is captured. But as they leave the house he breaks away from Holmes and again enters his stronghold, sinking the house and disappearing from sight. A terrific explosion tells those on the shore that the villain has used one of the bombs which he had hidden within, thus ending his career of crime.