Three women, last seen walking home alone at night, have been murdered in five weeks. The killer, Graham Shand, removes a necklace from the latest corpse to give his unfaithful wife Linda for her birthday before striking again. He is a failed taxi driver with a virility problem and Luther eventually traps him – after spotting the tell-tale necklace on Linda – with the aid of undercover decoy Layla, though it is Linda who has the last word. Elsewhere, Alice, still running free despite being a prime suspect, kills Henry Madsen to ‘save’ Luther.