简介：TheTARDISmaterialisesinEnglandinthe1970sandthetimetravellersmeetagirlnamedIsobelwhoseuncle,computerscientistProfessorWatkins,hasrecentlygonemissing.TheDoctorofferstohelptrackhimdown,startingattheplacewherehelastworked-theLondonHQofInternationalElectromatics,theworld'smajorsupplierofelectronicequipment. HisinitialsuspicionsaboutIE'smanagingdirector,TobiasVaughn,areconfirmedafterhebecomesreacquaintedwithLethbridge-Stewart,nowpromotedtoBrigadierandinchargeoftheBritishbranchoftheUnitedNationsIntelligenceTaskforce(UNIT),andlearnsthattherehavebeenotherdisappearancesatIEpremises. HediscoversthatVaughnisinleaguewiththeCybermeninaplantoinvadeEarth,butisalsoplottingagainstthemwiththeaimofseizingpowerforhimself.WatkinsisbeingforcedbyVaughntodevelopthecerebrationmentor,amachinedesignedtogenerateemotionalimpulsesasaweaponagainsttheCybermen. TheCybermenimmobilisemostofEarth'spopulation-sendingahypnoticsignalthroughspecialcircuitsincorporatedinallIEequipment-andlaunchtheirinvasion.TheDoctorhasmanagedtoprotecthimselfandhisfriendsfromthesignaland-withhelpfromanembitteredVaughn,whoiskilledduringthefighting-theinvasioniseventuallydefeated.…