When Vivienne Haldane is found murdered in her house she becomes the third victim of a serial killer who strangles married women with a silk stocking and removes their wedding rings after death - though the women are unknown to each other. Separated from her husband Mrs Haldane had a secret lover, referred to in her diary as 'X' and, like one of the other victims, she was seen getting into a green car. The stockings are a unique brand, Le Minou Noir, and have only one retail outlet in Oxford, Burridges department store. Here Thursday is shocked to find that widowed Italian saleslady Luisa Armstrong is a former partisan he met in the war but believed to be dead. Morse interviews the stockings' supplier, shifty Joey Lisk, who had tried to come on to Gloria Deeks, a prisoner's wife and assistant at the store, where she has many admirers. With the discovery of a fourth corpse evidence seems to point to Lisk but when simple store-man Norman, who worshipped Gloria, is also slain, it becomes clear that somebody at Burridges is the real killer out to frame Lisk.