On
December 29, 1940, during the
London Blitz, an elderly
Dr. John Watson tells his nurse the tale of an unrecorded case he shared with his friend
Sherlock Holmes. On May 19,
1882, a royal
treasury ship is destroyed by a monstrous
giant octopus on the coast of
Newhaven. Holmes and Watson investigate the shipwreck and do not believe the first-hand accounts of the sole survivor of the attack, but nonetheless investigate.
Inspector Lestrade states that he has recently had contact with Holmes' estranged brother Thorpe, a former partner of Lestrade's who was paralyzed during a
bank robbery seven years prior. In
Whitechapel, a young man is killed by a
Megalosaurus. Watson is skeptical until he and Holmes discover the creature on their morning constitutional. Finding escape, several more clues lead Holmes to deduce that the monsters are artificial, built by a criminal genius to acquire resources. On the case, the dinosaur steals a water pump operating a fountain and rolls of copper wire, presumably in order to create another monster. The octopus that destroyed the ship earlier is linked to the dinosaur because they are both similarly "exceptionally improbable". Lestrade accompanies Holmes and Watson during their investigation. On one of their leads, Lestrade ends up missing. Holmes's reasoning leads himself and Watson to an old
castle in Helmsmouth he and his brother visited as children. They come across another monster, a masked mechanical man:
Spring-Heeled Jack. Spring-Heeled Jack is revealed to be Holmes' brother, Thorpe, who also assumed the identity of a patient of Watson's. Inesidora Ivory, his accomplice, is with him. Thorpe explains that he built a mechanical suit to cure his paralysis, and he deduced that the crippling bullet ricocheted off a doorframe, fired by Lestrade. He plans to destroy London, assassinate
Queen Victoria and force Lestrade to claim responsibility. Ivory is revealed to be one of Thorpe's creations and his lover, and she carries a bomb in her workings that will detonate when she reaches Buckingham Palace, while Thorpe pilots his most complex invention yet; a fire-breathing
dragon in which he pilots and holds Lestrade hostage. Watson is sent to stop Ivory from killing the Queen, while Holmes pilots another one of Thorpe's flying inventions in an attempt to stop his brother. Thorpe's dragon sets fire to
Parliament and
Westminster Abbey. Ivory is deactivated by Watson moments before the explosion can take place and the dragon is sent crashing in the garden outside the Palace. Thorpe, crippled again, crawls from the wreckage and tries to shoot Watson, before he himself is shot by Sherlock Holmes. Holmes proves Lestrade was not responsible for Thorpe's crippling. Lestrade takes credit for saving the Queen and Holmes and Watson vow never to speak of the events again. In present time, Watson expires peacefully and his nurse visits his grave. Nearby, Ivory is visiting the grave of Thorpe Holmes. ==Cast==