World War Three ( TV story ) World War Three was the fifth episode of Series 1 of " Doctor Who " . The episode concluded the story begun in " Aliens of London " . It was notable for featuring the first instance of Mickey Smith actively assisting the Doctor , and therefore behaving like a companion , something that he would eventually become in due time . It suggested a bright political future for Harriet Jones , something that the Tenth Doctor would later actively change about the timeline in " The Christmas Invasion " . It was also the first time in the history of " Doctor Who " that the Doctor ' s TARDIS was shown to have a working telephone — something that would feature much more prominently throughout the Steven Moffat era — the Russell T Davies era of the show preferring to use the mobile phone Martha Jones gave to the Tenth Doctor in " Last of the Time Lords " . Synopsis . With the threat of interplanetary war looming , the human race prepare for the end , little knowing their enemies lie at the heart of the British government . As the Ninth Doctor , Rose Tyler and new friend Harriet Jones battle for their lives in 10 Downing Street , the Slitheen family set their plans for the destruction of Earth into motion . With the world changing around him , the Doctor is powerless , and it seems only Mickey Smith can save the world . . . Plot . Deadly electricity courses through all of the alien experts in the room , killing them , but the Ninth Doctor , not being human , is not as affected as the rest . The Doctor grabs his own electrified identity badge and attaches it to the collar of the Slitheen that was masquerading as Asquith . Somehow , as the electricity courses through Asquith , it affects Green , Blaine and the police inspector threatening Jackie as well . The Doctor makes his escape , running down and attracting the attention of the Metropolitan Police squad below . Mickey comes into Jackie ' s flat and sees the police inspector alien paralysed by electricity . He knocks it aside with a chair and grabs Jackie ' s hand , pulling her out of there — but not before taking a photograph of the alien with his mobile phone . Harriet and Rose rush past the writhing Margaret Blaine alien , running down the corridors of 10 Downing Street . Green struggles and manages to remove the badge from Asquith ' s neck , and they hurriedly scramble into their skins just as the Doctor returns with the police squad . The Doctor tells the squad that the Acting Prime Minister is an alien , but is met with obvious disbelief . Green accuses the Doctor of having killed all the experts , and Asquith orders the police , under authority of the Emergency Protocols , to execute the Doctor . The Doctor , apparently backed against a wall , says , " If I was you , if I was going to execute someone by backing them up against the wall , between you and me , a little word of advice — don ' t stand them against the lift ! " and ducks into the lift before they can shoot him . He rides it up to the top floor . Blaine continues to chase Harriet and Rose through No . 10 , and the two seek refuge in one of the offices on the upper floor . In the meantime , Asquith tells the police to isolate the upper floors , and he and Green ride upstairs in the lift , removing their skins . They join Blaine , who is enjoying the hunt , and they sniff out Harriet and Rose ' s hiding places . They are about to strike when the Doctor comes in , spraying the Slitheen with a fire extinguisher , causing enough of a distraction for Harriet and Rose to duck around the aliens . They run towards the Cabinet Room to get the Emergency Protocols to see what procedures they have for fighting aliens . The Slitheen are just about to follow them in , when the Doctor grabs a bottle of port from a side table , threatening to use his sonic screwdriver to " triplicate the flammability " of the alcohol . He asks them who they are and why they are invading . The Slitheen , held at bay for the moment , say that they are not invading , and the Slitheen is not the name of their species , but their family . They are here for business reasons , but before the Doctor can get them to tell what that is , the Slitheen realise that the Doctor ' s threat is a bluff . They prepare to end the hunt , but the Doctor observes that the Cabinet Room has a special feature — three - inch thick steel walls that can seal off the room , making it the safest place in Great Britain . He does just that , shutting the Slitheen out . . . but also cutting off any avenue of escape . Satisfied that the Doctor no longer poses a threat , the Slitheen summon the rest of the family to Downing Street , and Asquith orders Price to keep the ground floor secure and await an emergency address from the Acting PM to the people of the world . Outside , Andrew Marr tries to make sense of the variety of people who are showing up : Group Captain Tennant James of the RAF ; Ewan McAllister , Deputy Secretary for the Scottish Parliament ; even Sylvia Dillane , Chairman of the North Sea Boating Club . All they seem to have in common is their remarkable girth and the fact that they ' ve been invited to the upper levels of 10 Downing Street . They are all Slitheen in disguise , and when they get upstairs , they strip off their skin suits . Meanwhile , Mickey and Jackie have managed to make their way back to his flat , but the Slitheen who was Police Commissioner Strickland is still in pursuit , using his sense of smell to track Jackie . In the Cabinet Room , the Doctor puts the Prime Minister and Ganesh ' s bodies in the cupboard , and then checks for possible escape routes . Rose wonders how the Slitheen can fit inside smaller human skins . The Doctor explains that it is a function of the collars they wear — a compression field shrinks them down , leading to the gas exchange that causes their flatulence . The Prime Minister ' s skin was too small , even for them , which is why they did not use him as a disguise . The Doctor wonders why he finds Harriet Jones ' s name so familiar . Harriet says she is not famous , but just a lifelong backbencher . The Emergency Protocols list all the people who could help , but they are all dead downstairs . Rose wonders if the Protocols have defence codes that they can use to launch nuclear weapon s at the Slitheen . Harriet explains that due to the United Kingdom ' s past record , the release codes for a nuclear strike are in the hands of the United Nations , and a resolution has to be passed before the authorisations can be released . As they wonder what the Slitheen could be after , Rose ' s mobile phone beeps . It is Mickey , and he has sent a picture of the Slitheen in Jackie ' s kitchen . Despite his dislike of Mickey , the Doctor admits that he needs him . He asks Mickey to go to the computer and log on to the UNIT website , using the password " buffalo " to gain access . As he does so , Jackie takes over the phone , pointedly telling the Doctor how dangerous his life is , and asking him if he can promise her that Rose will be safe . The Doctor does not answer . Once in , Mickey finds the signal that the Slitheen ship in the North Sea is pulsing out into space . The Doctor puts Mickey on the speakerphone and tries to decipher the signal . The doorbell to Mickey ' s flat rings and Jackie goes to answers it . It is Slitheen inspector Strickland , who unmasks and starts to break through the door . Mickey offers to fend off the alien with his bat . Desperately , the Doctor and the others try to gather the information they know about the Slitheen so he can identify their race and hopefully their weakness . The various characteristics they have exhibited , including the fact that their gas smells like halitosis — calcium decay — helps the Doctor narrow it down to one planet — Raxacoricofallapatorius — and identify them as creatures of living calcium , which will be weakened by the compression . As the Slitheen crashes into the flat , the Doctor tells them through the phone to get into the kitchen and find anything with vinegar in it . Jackie dumps as many pickled foods into a measuring cup as she can and hurls the mixture at the Slitheen as it comes through . The acetic acid reacts with the creature , and it explodes . In Downing Street , Green and Asquith sense the death of their brother . Green steps out onto the street and speaks to the media as Acting Prime Minister . He informs them of the death of the experts at the hands of aliens and that there are " massive weapons of destruction " capable of being deployed within 45 seconds above their heads . He urges the UN to pass a resolution and release the access codes that will allow the UK to launch a pre - emptive strike against the alien mothership . The Doctor , listening to the broadcast over Rose ' s phone , knows that Green is lying . He realises that is why the Slitheen made such a spectacle out of the crash — not just to attract the experts but to panic the world and make it more likely for the United Nations to acquiesce to Green ' s request . He unseals the room long enough to confront the Slitheen outside . They will launch the missiles not into space but against other nations , triggering World War III . The Slitheen will then sell off the radioactive remains of Earth to the rest of the galaxy as a fuel source . The signal from their ship is an advertisement that the planet is for sale . The Doctor tells the Slitheen he will stop them . Blaine sneers , expressing disbelief that he could do anything whilst sealed inside the room . The Doctor says grimly , " Yes . Me . " He seals the room again , as uncertainty flickers across Blaine ' s face , her confidence shaken by the Doctor ' s demeanour . As morning breaks over London , the streets are deserted . The Slitheen gather , unmasked , in the Prime Minister ' s office to await the call from the UN Security Council . Jackie calls the Doctor , and says there must be something he can do . The Doctor reluctantly admits there is an option , but he cannot guarantee Rose ' s safety . He could save the world , but he could lose Rose . Jackie protests , but without even hearing what the option is , Rose tells the Doctor to just go ahead and do it . Harriet steps in at this point and , as the only elected representative in the room , orders the Doctor to take action . The Doctor tells Mickey to use the " buffalo " password to access the Royal Navy ' s systems . Mickey locates the HMS " Taurean " , a Trafalgar class submarine off the coast of Plymouth , and under the Doctor ' s instructions , remotely selects and launches a harpoon missile . The missile streaks inland , on a direct course for 10 Downing Street , as the UN concludes their debate . Persuaded by the " proof " that the UK has provided , they agree to release the nuclear missile codes . The missile is picked up on radar , but Mickey stops the counter measures taking effect . The Doctor , Harriet and Rose take refuge in the cupboard , hoping to ride out the explosion . The police squad sergeant orders the evacuation of 10 Downing Street and goes upstairs to warn Green . When he sees the Slitheen in their true forms , he makes a hasty retreat . The surrounding streets are cleared as the missile starts its final descent , and as the Slitheen still scramble around trying to get into their skins , 10 Downing Street is reduced to rubble . Thanks to the small and sturdy walls of a cupboard , Harriet , Rose and the Doctor " ride out " the blast and survive . The Slitheen are not so lucky . Harriet wonders how they will rebuild from this , and the Doctor suggests that she become Prime Minister . She goes off to speak to the press and emergency services , announcing proudly that the crisis has passed ; mankind stands tall , proud and undefeated . As he and Rose leave quietly , the Doctor remembers now why Harriet ' s name was familiar . Harriet Jones will be a future Prime Minister , elected for three successive terms , and the architect of Britain ' s Golden Age . Rose goes back to Jackie ' s flat and watches the aftermath on television . Jackie grudgingly admits that she can ' t get rid of the Doctor now since Rose is so infatuated with him , something which Rose denies . Jackie offers to cook for the three of them and get to know the Doctor better . The Doctor calls Rose on her mobile phone from the TARDIS , where he is cancelling the Slitheen " advertisement " . When Rose tells him of her mother ' s offer , he refuses — Rose can stay there if she likes , but he has a universe to see . Jackie sees Rose packing and asks her not to go , but Rose doesn ' t answer . The Doctor has caught the hooligan boy that defaced his police box with the words " BAD WOLF " and made him clean off the spray - paint with a bucket of water and a scrubbing brush . With his misdeed amended , the kid is given a final scolding by the Time Lord : " Good lad . Graffiti that again and I ' ll have you . Now , beat it . " As the boy scampers away , Mickey stops by and speaks to the Doctor by the TARDIS . Mickey cannot believe that the papers are already saying the whole incident was a hoax . The Doctor gives Mickey a compact disc containing a computer virus that will wipe all trace of the Doctor ' s presence on the Internet , and asks him to use it . He also offers Mickey a place in the TARDIS , but Mickey says that the Doctor ' s world is not for him . He asks the Doctor not to tell Rose he said this , however . Rose arrives with a backpack full of her belongings , tossing it to the Doctor and playfully telling him that he is now stuck with her . Rose says goodbye to Mickey and Jackie , assuring her mother that the TARDIS is a time machine — she can travel all over the universe and be back within ten seconds . Rose asks Mickey to come along with them but the Doctor , following Mickey ' s wishes , pretends that Mickey is not welcome . Rose and the Doctor enter the TARDIS and it dematerialises . Jackie waits ten seconds , but it does not return , and she walks back towards her flat . Mickey unfurls his newspaper about the aftermath of the recent crises , planting himself on a rubbish bin . He stays in the street , and continues to wait . Story notes . Filming locations . " to be added "