fourth episode fourth series british science fiction television series doctor depicts adventures time travelling alien known doctor episode broadcast bbc april episode sequel poison sky written previously wrote linked episodes manhattan evolution series features appearance alien series story doctors companion seen time lords episode takes place present day earth martha unit summon doctor assistance concerning atmospheric omission system revolutionary piece green technology installed million cars worldwide later revealed plot poison atmosphere runner considered making return revival series wanted changes martha personality departure episode viewed million viewers original broadcast appreciation index critics gave generally positive reviews praising return portrayal writing stated improved previous episodes plot companion doctor calls ask assistance investigation unit unified intelligence minutes doctor craft tardis contemporary britain martha raid factory doctor introduces companion martha unit instantly befriends martha concerned unit ethics asks doctor associated doctor replies work 70s 80s marketing satellite navigation system developed young system reduces carbon dioxide emissions zero unit requested doctor help technology contemporary alien unit concerned simultaneous deaths occurring spontaneously days earlier doctor travels private school investigate system discovers recent events plotted alien warrior race known led undefeated instead outright invasion taking control combination human clones mind control martha captured controlled humans provide mole unit returns home warn mother grandfather doctor having advised martha concerned implications telling truth decides warning mother doctor investigates device attached car discovers secondary function device poisonous gas attempts car road trapped million devices installed cars worldwide episode cliffhanger depicts shouting help doctor street cars gas ship planet prepare battle production conception episode features return appeared serial doctors central appearance unit appeared time lords special guest appearances episodes reset dead man walking day death brief executive producer gave writer included terms military martha episode continues pattern having monsters classic series return new davies commented list villains time location episode chosen previous story set earth writing martha departure allowed davies change character personality mature equal doctor opposed series love writers debated aspects character status reaction particular elected emphasise martha medical career military career avoided dawn scenario felt initial opinion companion second series episode school reunion episode major appearance unit revival changed unified intelligence request united_nations cited political climate potential brand confusion reasons new acronym coined davies meetings unit gray wilson specifically written alien fodder episode refers inconsistencies dating unit stories doctor unsure worked unit 1970s 1980s initially envisioned poisonous gas emitted factories changed later drafts cars reasons episode provide social commentary idea evil system irresistible davies thought concept doctor series produced order subplot seeded previous episode partners crime fifteenth broken moon mentioned previously mentioned time lords partners crime fires episode system installed unit explodes originally wanted large explosion reduced explosion sparks reduce costs action movie cliché episode like aliens london experiment properly introduces lead companion family unlike tyler jones families met doctor runaway bride voyage damned respectively providing additional subplot dialogue explains absence runaway bride character having spanish flu positive opinion doctor different according joined long line mothers don doctor davies wanted family member trusted doctor revival filming opening scene depicts system driving reporter canal filmed cardiff docks scene time car cannon required completed shot car fired canal removed immediately clear shipping route scenes filmed country park october london skyline gas added post production mill interviewed friday night stated filming alongside actors playing weeks realised actors inside costumes assumed ran electricity actor removed helmet reveal real face realised mistake stated said nearly died despite clone culture asserted classic series episode depict process originally factory workers clones reduced martha solve continuity problems second template clone portrayed wore prosthetic mask took longer apply previously worn scenes involving tank filmed welsh factory reused prop fires tank contained clone davies enjoyed scenes set room liked playing evil companion davies felt real martha warmer davies thought gray harris discovering tank room classic doctor broadcast reception broadcast ratings watched programme timeslot million viewers episode second watched programme day beaten britain seventeenth watched programme week episode appreciation index considered excellent highest figure recorded critical reception stage commented overall episode old fashioned new gets stating script simple premise makes wonder didn think character moved away caricature runaway bride wright praised portraying martha evil counterpart fan wright reacted positively return redesign digital spy rated episode stars felt narrative plotted paced felt writing improved manhattan praised unit martha family interaction martha portrayal felt voice distinctly episode direction received criticism particularly scenes clone room end felt effectiveness lies viewers wish tune poison sky ign rated episode good stating despite episode premise came close greatness praised script walked balls sci wales noted perpetual swings square mess audience expectations ryan performance praised wales felt displayed charisma range dead fish despite martha transformation esque super soldier wales summed episode pretty opener swiftly shifting pieces place week inevitably showdown alpha called exciting nostalgic adventure said episode lives reputation transforming normal object case car global killer bear praised episode martha introduction opposite school reunion providing human element subplot visits grandfather episode cliffhanger bear wrote took long point criticized bland dialogue simplicity mind control felt reduced intricate story piece saturday morning cartoon material thought episode lived expectations sharp dialogue humour plotted story good pace overall action despite episode slow start praised unit old tired unit newly revamped unit lots cool doctor meeting calling scene inspired piece writing episode cliffhanger calling best believed idea worked weak spot noted appeared previous appearance stating shoot ask questions later reviews poison sky reviews
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