Caught by the Slitheen at 10 Downing Street, the Doctor manages to break free from the electrocution trap, using his ID card against his Slitheen captors by sabotaging their compression mechanisms. The feedback also allows Jackie to escape as Mickey breaks into her flat to save her, while Rose grabs Harriet Jones and escapes the Cabinet chambers, leaving Indra's dead body behind. The Doctor brings the Prime Minister's soldiers into the audience room, but the Slitheen has managed to climb back into the body suit of General Asquith and he and Green turn the tables on the Doctor.
Several Slitheen pursue Rose and Harriet through the halls of 10 Downing, while the Doctor narrowly escapes while backing into a lift. On the upper floors, Rose, Harriet and the Doctor are reunited, escaping their pursuers to the Cabinet room, which is protected with a reinforced steel frame designed to withstand bombardment. They lock themselves in the Cabinet room, after discovering that the Slitheen – their family name, not their race – are scavengers, come to Earth to blow it up and sell off the radioactive debris to high bidders for fuel.
More members of the government arrive – all Slitheen, the rest of the family, save one… the one occupying Strickland's body suit, pursuing Jackie and Mickey. They contact the Doctor on Rose's altered mobile phone, but are attacked by Strickland. Harriet helps the Doctor pinpoint the homeworld of the Slitheen through the calcium gas emissions they exude, allowing Jackie and Mickey to escape into his kitchen and throw vinegar at Strickland, which causes the Slitheen to explode.
Joseph Green calls a press conference to request that the United Nations release launch codes to the UK for weapons of mass destruction to launch at the æalien threat.' While the UN considers the situation, Green, Asquith and Margaret Blaine call their brethren together to escape to their private ship – the weapons will be turned back on the planet to destroy it. The Doctor realizes there is only one way out of this, but it will endanger Rose's life, something Jackie protests until Harriet, realising she is the sole ranking member of the British government, makes the decision for him to act. The Doctor has Mickey use his secret connections into the UNIT website to activate a defensive missile, aiming it toward 10 Downing. The soldiers escape, while the Slitheen, awaiting their departure in the Prime Minister's office, are hit with the missile, which destroys 10 Downing… however, the Doctor, Rose and Harriet, deep within the reinforced Cabinet bunker, escape unharmed. As Harriet goes off to calm the press, the Doctor finally remembers why he knows her name: she will later become a three-term Prime Minister and the architect of Britain's golden age.
Jackie begins to accept that Rose is going to leave again, so she invites the Doctor over for dinner, but the Doctor refuses… he doesn't want to establish ties here. He returns to their neighborhood, where he gives Mickey a CD which will launch a virus to destroy any trace of the Doctor's existence remaining from Clive's website and other sources; he also offers him a place in the TARDIS, realizing Mickey's not the idiot he'd thought he was. While Mickey refuses politely, needing to stay behind and look after Jackie – and unable to cope with the danger – Rose returns to the TARDIS with her belongings, this time not for just temporary passage, but as a permanent addition to the crew.
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