“Natural causes,” the doctor wrote on 40-year-old Vera Sidney’s death certificate on Friday, February 15th, 1929. Vera, who lived in Croydon, Surrey, had been ill for only a few days. It was the second family tragedy in less than a year – her brother-in-law, Edmund Duff, 59, had died only 10 months earlier. He also lived in Croydon, and in his case too death followed a few days’ illness.

Less than a month after Vera’s death, her mother, Mrs. Violet Sidney, also of Croydon, died, again after a short illness. She was buried, but local gossip reached such a crescendo that all three bodies were exhumed. All three were found to contain much more than their fair share of arsenic.

That suggested they must have been despatched by a family member. But who? Chief suspect was Edmund Duff’s widow. The story went that she was having an affair and poisoned her husband to be rid of him. Having got away with that murder she was said then to have poisoned Vera and Violet for financial gain.

The woman died in 1973 aged 87. Did she take the secrets of the triple murder with her to the grave?