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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.