The murders are committed by Ruth Astor, a telephone operator who was gang-raped by members of an elite Oxford dining club known as "The Berserkers". Ruth uses her position at the switchboard to track these men through their calls to a high-class call girl, Eve Thorne, staging their deaths as poetic, artistic retribution for her trauma. Themes of Institutional Change
Joan's sudden reappearance in Oxford throws Morse into emotional turmoil, reopening wounds from his failed marriage proposal in the previous season.
A subplot involving the theft of a Fabergé egg, "Nastya’s Egg," serves as a metaphor for fragility and the corruption hidden behind academic prestige. The egg is ultimately passed to Eve Thorne as a "new life," symbolizing a desperate hope for escape from a cycle of exploitation.
A significant backdrop to the mystery is the restructuring of the Oxford police into the Thames Valley Constabulary.