In the second half of the two-parter, Mickey (Noel Clarke) defends his girlfriend’s mother Jackie Tyler (Camille Coduri) from an alien Slitheen dressed up as a police inspector. Meanwhile, the Doctor (Christopher Eccleston) escapes electrocution at the hands of the Slitheen who are posing as the UK government. He brings the police, but by then the aliens are back in their human suits. He flees to the upper floors of Downing Street to meet with his companion Rose Tyler (Billie Piper) and the real minister Harriet Jones (Penelope Wilton) in the cabinet rooms. The Slitheen family are on Earth to steal the planet and sell it off piece by piece.

The Doctor contacts Mikey and tells him how to log onto the UNIT website. He learns that the real Slitheen ship is in the North Sea, emitting a signal. He also learns that the Slitheen are affected by acetic acid, so Jackie and Mickey use pickled eggs, pickled onions, and gherkins from Mickey’s flat to kill the Slitheen posing as a cop.

The Slitheen in control of the government declare a national security emergency and ask the UN to release the nuclear codes to attack the fake alien threat, though the Doctor knows they are trying to start World War III. When the Earth is radioactive rubble, it will make a nice profitable fuel source for alien ships. Harriet insists the Doctor help Mickey to hack into the controls of a Royal Navy nuclear submarine and fire a missile at 10 Downing Street. The Slitheen are killed, but our heroes are in the reinforced Cabinet Room and are not harmed.

Since the PM is dead, the Doctor suggests Harriet become Prime Minister. He then gives Mickey a CD to upload into the Internet which will erase every mention of the Doctor on the Web. He offers to take Mickey with him and Rose in the TARDIS, but he is too frightened. The Doctor and Rose leave together.

The episode was—no surprise—declared to be on the silly side and received mixed reviews. Lachele Carl appears as American reporter Trinity Wells, who also appeared in five more Doctor Who episodes, and in two spinoff series—Torchwood and Sarah Jane Adventures. The Slitheen are from the planet Raxacoricofallapatorius. The Doctor says that vinegar will kill the Sitheen “just like Hannibal” crossing the Alps. Hannibal’s soldiers had built fires on the large rocks blocking their way, then doused them with vinegar, which made them split into smaller rocks that the troops could remove.