Aliens of London ( TV story ) Aliens of London was the fourth story in the first series of " Doctor Who " . It was notable for featuring the first cliffhanger in the BBC Wales run , by virtue of starting the first two - part story . Keeping cliffhangers in the show allowed Davies to expand the plot and restore a well remembered part of the original series . Narratively , the episode had several introductions . It introduced the Slitheen , who would return to " Doctor Who " and " The Sarah Jane Adventures " . It also marked the first appearance of Toshiko Sato , who would later feature as a regular character on " Torchwood " , and as she later revealed herself to be an acting member of Torchwood Three at the time of her first appearance , this was technically the earliest instance of the presence of the Torchwood Institute seen in " Doctor Who " , though the organisation would not be explicitly named and introduced until TV : " Bad Wolf " . In addition , this episode introduced another recurring character , British politician Harriet Jones . It also introduced UNIT to the revived series . One of its legacies — sometimes forgotten by writers — was offered in its pre - title sequence . As the Ninth Doctor mistakenly brought Rose Tyler one year into the viewer ' s future , the " present day " of " Doctor Who " and its two BBC Wales spinoffs were generally considered to be one year later than the year of initial broadcast . It was also the final episode of " Doctor Who " to have any portion recorded at BBC Television Centre . Synopsis . Rose returns home to discover that she has been missing for a whole year , although for her , it ' s been a couple of days . However , before she can explain her absence , a spaceship crashes into Big Ben , causing a worldwide crisis . Worse still , the Prime Minister has mysteriously disappeared . . . The Doctor ' s investigation puts him in the spotlight with the British government , as his long history of defending Earth finally catches up with him . But there are sinister goings on at 10 Downing Street , and politician Harriet Jones ' quest to get some answers brings her into a brave new world . . . of aliens . Meanwhile , Rose finds trouble closer to home , as her past mistakes threaten to tear her family apart . Plot . Rose and the Ninth Doctor have returned to the Powell Estate . Rose , thinking she has only been gone twelve hours , heads off to see her mum . Meanwhile , the Doctor notices a poster depicting a missing girl . Jackie is shocked to see Rose . As she hugs Rose , the Doctor enters and informs Rose that she ' s been gone twelve months , not hours . Jackie has been frantic with worry , but now she begins to scold Rose for not getting in touch with her . Interviewed by a police man , the Doctor says that Rose is his companion . After an argument Jackie slaps the Doctor . Later , Rose and the Doctor chat outside . Rose can ' t tell her mother about what she has done . Both are shocked to see an alien spaceship pass overhead and clip Big Ben before crashing into the river . Rose and the Doctor try to visit the scene but are prevented by traffic . They head for home to watch the news on television . Several people are visiting , while the Doctor tries to watch the news . He sees General Asquith entering the hospital where the alien has been taken . The news also reports that the Prime Minister is still missing . At the hospital mortuary , Dr Sato performs an autopsy on the alien . Meanwhile , several important figures gather at 10 Downing Street , including Joseph Green . He is informed by Indra Ganesh , the junior secretary , that he is acting Prime Minister for the crisis . As Ganesh attempts to lead Green away , he is accosted by Harriet Jones , MP for Flydale North , who wishes to meet with the Prime Minister but is brushed off . Green meets with Margaret Blaine and is given the emergency protocols . The Doctor decides to leave the party , giving Rose a TARDIS key before he leaves . Mickey arrives , and Rose learns that several people , including Jackie , had suspected him of murder ing Rose . The Doctor uses the TARDIS to get to the hospital . He accidentally walks into a room of soldiers , but when they hear screaming , they all run out of the room and the soldiers listen to the Doctor ' s orders . He finds Dr Sato , who says that the " dead " alien is alive and has run off . Despite the Doctor ' s command , one of the soldiers shoots the alien dead . Back in the Cabinet Room , General Asquith meets with Green and Blaine , who are acting strangely . He attempts to relieve Green of command , but Green , Blaine and another man , Oliver Charles , unzip their foreheads . Asquith screams . Unknown to them , Harriet Jones has sneaked inside the room and watches them from her hiding place . The Doctor informs Dr Sato that the " alien " is fake . He then leaves . Outside , as Mickey is gloating that the Doctor has left Rose , the TARDIS materialises and the Doctor is back . After Jackie sees the TARDIS interior , she goes upstairs and calls a number to report the Doctor . The Doctor deduce s that the spaceship landing was faked as well . It originated from Earth , and whoever did it has been here for a while . He notes that UNIT has been called in to deal with the crisis . The trio of Green , Blaine and Asquith complain about compression and gas exchange . They receive a code nine — the Doctor , an expert in extra - terrestrial affairs , has been located . When they step out of the TARDIS , they are surrounded by police and helicopter s . Mickey runs away , and the Doctor and Rose are arrested . They are taken to Downing Street , where the Doctor is brought in to meet with the other experts . Rose does not have proper clearance , so Harriet offers to stay with her . Meanwhile , a policeman visits Jackie for information . The experts are gathered with Green and Asquith in a small room . Harriet takes Rose to the Cabinet Room and tells what she saw — Green and Blaine are aliens in skin suits who killed Asquith and the Prime Minister . The Doctor figures out why the spaceship crash was faked — to get the Earth ' s experts in one place . The policeman visiting Jackie begins to unzip his forehead . Ganesh , Rose and Harriet are caught by Margaret Blaine , who unzips her forehead . In the room below , Asquith unzips his forehead , and Green uses a remote control to electrocute the experts . They announce themselves as the Slitheen . Story notes . Myths . None