"Army of Ghosts" is the twelfth and penultimate episode in the second series of the British science fiction television programme Doctor Who which was first broadcast on 1 July 2006. It is the first episode of a two-part story; the concluding episode, "Doomsday", was first broadcast on 8 July.

The episode takes place on contemporary Earth, some time after the Doctor's and Rose's last visit to Earth in "Love & Monsters". During this time, the public have become accustomed to intermittent appearances of ghosts. The Doctor tracks the source of the ghosts to the Torchwood Institute, where the Doctor learns of the Cybermen from "Rise of the Cybermen" and "The Age of Steel" crossing a breach in the Void created by a Dalek-piloted Void ship.

The episode begins with a cold open in which Rose, via narration, recollects her life with the Doctor and her belief that they would always be travelling together. She then mentions that this episode is "the story of how I died".

Rose Tyler and the Doctor decide to visit Rose's mother Jackie. Jackie is pleased to see them, but makes a strangely happy remark that her deceased father will be joining them shortly. Despite Rose's protestations that her grandfather is dead, Jackie insists that he has returned and has been visiting her for some time. A vaguely humanoid and luminous silhouette appears in the flat, surprising both the Doctor and Rose but delighting Jackie before disappearing. TV broadcasts confirm that this is a worldwide phenomenon and Jackie explains that a few months previously millions of ghosts began appearing all over the world. Humans have come to accept them and believe that they are the manifestations of loved ones.

The Doctor dismisses the possibility that these are ghosts and conducts an experiment with the help of the TARDIS. He attempts to trap a ghost and determines that they are not ghosts but are impressions of something forcing its way into this universe. The Doctor tracks the signal back and uses the TARDIS to travel there, arriving at the Torchwood Institute. The Doctor introduces himself and tells everyone that Jackie is Rose, his companion. They are taken by soldiers to see Torchwood's current director Yvonne Hartman, while the TARDIS is impounded with Rose inside. Ms. Hartman shows the Doctor the source of the ghost energy, an invisible breach in the universe through which a mysterious spherical object has arrived. The Doctor inspects the sphere, declaring it to be a "Void ship"—which, according to him, is impossible. It is designed to exist in the space between universes, a nothingness called the Void. The ship is completely undetectable by all scientific instruments. Torchwood has no explanation for the sphere is or how it got there, but they claim responsibility for the ghosts. Torchwood has been conducting experiments on the breach, forcing it open in an attempt to harness it as a source of energy. Ms. Hartman also reveals to the Doctor that his encounter with Queen Victoria in "Tooth and Claw" made him an enemy of the state and was the catalyst for the creation of Torchwood. Unbeknownst to all at this point, an unseen party has infiltrated the institute and has been successful in subverting three Torchwood staff.

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