AmericanpsychologistJohnHoldenarrivesinLondontoparticipateinasymposiumaimingtoexposewitchcraftanddevil-worshipasafraud,withattentioncenteredonacultrunbyaJulianKarswell.Debarkinghisplane,Holdenlearnsthatthesymposiumleader,HenryHarrington,hassuddenlydiedandheisnowincharge.WhatonlytheaudienceknowsisthatHarringtonwasclearlykilledbyademon,apparentlysummonedbyKarswelltoavengehispersecution.DespiteboththreateningandcajolingbehaviorbyKarswell,Holdendeterminestoproceed,thoughtheonlycultmemberwillingtotalkabouthisexperiencesisinaprisonpsychiatricward,catatonicafterallegedlykillingyetanothercultmember.However,Harrington'sniece,Joanna,believes,basedonheruncle'snotes,thatKarswellmayindeedhavesomesatanicpowersderivedfromanancienttomeinanobscurelanguagewhichhehasbeenabletotranslate,andattemptstowarntheskepticHolden.Karswell'smotheralsoattemptstowarnHoldenoff.However,thethingwhichbeginstomostgettoHoldenaretheoccasional,butmounting,sensoryandmentaldisturbanceshebeginsexperiencingafteranencounterwithKarswell,andthediscoverythat,duringthisencounter,KarswellsecretlyslippedaslipofparchmentwithacurseinrunicsymbolsonitintoHolden'sbelongings,aparchmentidenticaltooneHarringtonrecordedhavinghadpassedtohiminasimilarmannershortlybeforehisdeath...[N.B.HoldenatnopointstaysattheKarswellestate].
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