Morseistakenseriouslyillatamuseumreceptionandishospitalized.Inthehospital,Supt.Strange,visitsMorsetopushhimtotakeearlyretirement,whileDr.Millicent'Millie'VanBurengiveshimherbookona140year-oldcourtcaseknownastheOxfordCanalMurders.Thecaseinvolvedthemurderandrapeofayoungwoman,MrsJoannaFranks,travelingbycanalboatfromCoventrytoLondon.Thecaseresultedinthreeboatmenbeingsentencedtodeathandtwoofthemhanged.MorsestartstoreadMillie'sbookanddreamsaboutit.Hesoonhasanumberofproblemswiththecase. Whyweren'tthethreemenalsochargedwiththeftWhydidMrsFrankstakeaboatinsteadofatrainthatwasmuchfasterandcomfortableandonlyslightlymoreexpensiveWhydidn'tsheabandontheboataftershecomplainedaboutlewdbehaviorofthecrewattheshippingofficeinBanburyWhydidshethendrinkand'socialise'withthecrewWhathappenedtoher'carpetbag'withwhichshearrivedontheboatbutwhichwasnotmentionedinthecourtcase,norwasitstoredinthearchiveswithher,almostempty,trunkThetrunkwasmarkedwithinitialsofherfirsthusbandwhohaddied.Howdidithappenthathershoeswerefoundontheboatbutnobodysawherreturntotheboatfromtheforest PCAdrianKershawdoessomebrilliantlegworkforMorse.Hestudiedhistoryandhasinvaluablebackgroundknowledge.Forinstance,hementionsthattheboatmenhadbadreputationbecausetheyworkedonSundaysanddidnotattendchurch.LaterachapelwasbuiltfortheminOxford. Thedeadwoman'sclothesandtheshoesfoundontheboataresubmittedtomodernforensicinvestigation.Theresultisthattheshoesdidnotbelongtothedeadwomanfoundinthewaterbecauseshewasmuchtaller.Theshoeswereneverusedintheforest. OnlyMrsFranks'husband,CharlesFranks,wascalledtoidentifythebodyofthedeadwoman.Heclaimedthat,whileherfacewasdarkenedanddisfigured,hefoundabirthmarkbehindherear.Theprosecutorwelcomedthatinformationthatonlyahusbandoraloverwouldknow.Theaccusedwerenotshownthebody.Thedefenseattorneymerelyclaimedthattheguiltofthethreemenwasnotproved.Allthreeaccusedclaimedtotheendthattheywereinnocent.OneofthemwasnotexecutedbecauseheembracedChristianityinprison. MorseinstructsKershawtoinvestigateifCharlesFranksbenefitedfromhiswife'sdeathand,indeed,hepocketed300poundsinsurancemoney.CaseclosedCharlesFranksmurderedatallwomenanddroppedherinthecanalaftermeetingJoannaintheforest.IfJoannaFranksjumpedofftheboatatthesametimeasthedeadbodyhitthewater,sheswamtothebankandjoinedherhusband.Thecouplechangedtheirnames,inthecaseof'CharlesFranks'asecondtimeafterhe'died'asJoanna'sfirsthusband.Thefourthboatman,ayoungsterwhowasnotcharged,wasprobablypaidbyJoannatogivefalsetestimony. MorsetravelstoIrelandandhasagraveofJoanna'sfirsthusbandexhumed.Thecoffincontainsbagsofsandandsomestones.
