NewYorkprivatedetectiveDuncan"Mac"MacLainisblindbuthaskeenlydevelopedallhisothersenses.HepursueshisworkassistedbyhisfaithfulguidedogFriday,hisbutler,Alistair,andhisassistant,Marty.RetiredactressNormaLawry,anoldfriend,comestoMacseekingadvice.Herheadstrong17-year-oldstep-daughterBarbara,herselfapromisingactress,isenamoredwithherleadingmaninasmalltheaterproduction,themucholderLotharioPaulGerente.Paul,whohadoncebeenNorma'slover,hasconvincedBarbarathatNormaactuallywantsPaulforherselfandhasonlymarriedherfatherStephenforhismoney.AtMac'surging,NormatriedtoreasonwithPaul,butheinsiststhathelovesBarbaraandlaughsheroff.BarbaraisequallydisdainfulofherandagreestomeetPaulfordinnerthatnightathisapartment.
　　Norma'shusbandStephenLawryisascientistleavingthatnightonatriptotestasecretinventiononwhichhehasbeenworkingforthegovernmentandthewareffort.WorriedaboutBarbara,sheusesapretextnottoaccompanyStephenandgoestotheapartment.WhenBarbaraarrives,shefindsPaul'sdeadbodyandthinksthatNormahaskilledhim,eventhoughNormainsiststhathewasdeadwhenshearrived.BarbarathreatenstocallthepoliceunlesssheleavesStephen.Fearingthatascandalwillhurthim,Normaagrees.NormathenturnstoMac,whogoestoPaul'sapartmentwithFridayandMarty,onlytofindthebodyandtherugunderitmissing.AmanarrivestoreplacetherugandMachidesinacloset,overhearingatelephonecalltoNorma'snumberfrom"Gabriel"to"Vera."Macaccidentallygiveshimselfaway,butwithFriday'shelpoverpowersGabriel,whorefusestotalk.MachasMartyhidehimtokeephimunderwraps.
　　Normareturnstohercountryhomeunexpectedly,whichdiscouragesanespionageringthatincludesherbutler,Hansen,frombreakingintoStephen'ssafeandstealinghisplans.TheyhavekilledGerente,whowasalsoanagent,andhiddenthebody.MacarriveswithFridayatNorma'shouseandpretendstobehercurmudgeonly"UncleMac"whohascomeforavisit.HisblindnesslullsanysuspicionsHansenmighthaveabouthim.Shortlythereafter,Barbaracomeshomefroman"emergencyrehearsal",calledtogetheroutofthehousebyherdirector,CheliScott,whoinveiglesaninvitationtospendthenightattheLawryhome.UnknowntoBarbaraandNorma,Cheliistheringleaderofthespies.CheliorderedPaulkilledbecausehisaffectionforBarbarawasbeginningtolimithiseffectiveness,andsheimmediatelysuspectsMacisnotwhatheseems.
　　Gabriel'swifeVera,theLawrys'maid,isalsoapartoftheplot.WhenGabrieldoesnotreturnhome,Verabecomeshystericalwithworry.MacsecretlyasksVeratomeethiminthegreenhouse,usingherworryaboutGabrielasalure.Sheisobservedbytheothers,however,andiskilledbyHansenbeforeshecanreachMac.Thespiescutthehouse'stelephonewiressothatMacandNormacannotcallthepolice,andChelihasMaclockedupunderguard.Usinghisblindnessasadistraction,MacoverpowershisguardandreleasesFridayoutawindowwithinstructionsto"gohomeandgetMarty."StephenarriveshomeandChelithreatenshisfamilyifhedoesnotgiveherthefinalstepincreatinghisinvention,whichwasnotinthesafe.BarbarafinallyrealizeshowmuchNormaactuallycaresforher.Mactriestostallfortime,butislockedinthecellar.WhenHansengoestokillhim,Machasbrokenthelightbulbandhisadvantageoftotaldarknesshelpshimovercomethespy.MartyandFridayreturnwiththepolice.WhenFridayisspottedbyalookout,MacoverpowershimandissavedfrombeingshotbyanotherlookoutbyFriday.Afterthespiesarecaptured,StephenandNormaareofftoWashington,D.C.,withBarbararemainingbehindtocareforhernew"UncleMac."