Aliens of London

"Aliens of London" is the fourth episode of the first series of the British science fiction television show Doctor Who after its revival in 2005. First broadcast on 16 April 2005 on BBC One, it was written by Russell T Davies and directed by Keith Boak. It is the first in a two-part story, concluding with "World War Three".

The episode is set in London one year after the 2005 episode "Rose". In the episode, the alien crime family the Slitheen fake a spaceship crash-landing in the River Thames, putting the Earth on high alert. The Slitheen use the crashed spaceship to lure experts of extraterrestrial life including the "ultimate expert", the alien time traveller the Ninth Doctor (Christopher Eccleston), into a trap inside 10 Downing Street.

This episode introduced the character of Harriet Jones, played by Penelope Wilton, who would reprise her role in the episodes "The Christmas Invasion" and "The Stolen Earth". It also featured an appearance by actress Naoko Mori, who went on to feature in the spin-off Torchwood as a result of her performance. The Slitheen aliens are part-computer-generated imagery (CGI) and part-prosthetic/costume. "Aliens of London" was watched by seven million viewers on initial broadcast and received generally mixed reviews.

The Series wide arc of "Bad Wolf"s appearance in this episode comes in the form of Graffiti, Scribbled onto the side of the TARDIS by an Unnamed Child.