LewisreturnstoOxfordafterseveralyearsabsenceandisreluctantlyassignedbyhisnewboss,DCSInnocent,tothemurderofanOxfordmathematicsstudentwhowasshotwhileparticipatinginasleepstudy.Thekey-codeusedtoaccessthesleeplabwasassignedtoafellowmathsstudent,DanielGriffin,butDaniel'smathtutorhasprovidedhimwithanalibi.Danielisamaladjustedyoungmanwhowillsooninherithisfather'sautomotiveempire.Heisdisruptiveandhasnorespectforhisunclewhonowheadsthecompany.ThefutureofthecompanyhoweverrestsonanimpendingdealwithJapaneseinvestorswhoinsistthatfamilyunityisallimportantatthistime.Whentwoothermurderoccurs,Lewismustdecipheracrypticclueleftinanoldcasefilebyhisformerboss,ChiefInspectorMorse.