Britain’smostnotoriousserialkiller,DennisNilsen,confessedtokilling15peoplein1983.Overafive-yearperiod,hepickedupvulnerableyoungmen,luredthembacktohishomeandstrangledthem,beforedisposingoftheirbodiesunderthefloorboards.　　Thetruthabouthowandwhyhekilledhasbeenthesubjectofmuchspeculationinbooksanddocumentariesoverthedecadessince.Now,withuniqueaccesstoawealthofpersonalarchiveleftinhiscellafterhisdeath,includingover250hoursofnever-before-publishedcassettetapesofhisprivaterecordings,thisfilmwilltakeusintoNilsen’sworld.FromayoungboygrowingupinaquietScottishfishingvillagetoacold-bloodedmurdererprowlingthestreetsofLondon.　　Setagainstthebackdropof1980sBritain,whenmassunemploymentdrewyoungmentoLondoninsearchoftheirfortunes,onlytofindthemselvesdestituteandeasyprey,andweavingtogetherinterviewsfrompolice,journalists,survivors,bereavedfamilies,and-forthefirsttime-thekiller’sownvoice,thisfeaturelengthdocumentaryexploreshowNilsenwasabletogetawaywithmultiplemurdersandattacks,unchallenged,forfiveyears.

白人历史教师丹•邓恩（瑞恩•高斯林饰），在纽约布鲁克林一家破旧的公立中学教书，他的学生多是黑人。丹有激情和创造力，热爱学生，不遵循官方教学大纲，相信黑格尔辩证法，认为历史本质由相反力作用而成。他使得纸页间枯燥的历史生动鲜活，鼓励学生思考和分析历史，及自己周遍世界的运作法则，学生成为丹存活于社会的救生索。晚上，他是不可救药的瘾君子。　　这种分裂的生活没有能持续多久，丹某次在空无一人的女更衣室吸毒而虚脱，被他的黑人女学生德丽（莎莉卡•艾普斯饰）发现。共同保守的阴暗秘密，拉近了他们的关系，也改变了各自的生活。