Mary Elizabeth Cassidy was born in County Durham in 1893 and worked in service. She married John Knowles, a labourer, and lived with him at Windy Nook near Gateshead, along with a lodger, John Russell, for many years.
Knowles died in 1955 and Russell a few months later. She then married Oliver Leonard, an eighty-year-old retired estate agent, in September 1956; he died thirteen days later. In September 1957 she married Ernest Lawrence, a seventy-five-year-old retired engineer; he died in October. Each left her what he had, in sums between fifty and two hundred pounds.
What caught her was talk. At the reception after her fourth wedding she made a series of jokes about the catering, remarking of the leftover cake that it would come in handy for the funeral, and asking the undertaker whether he would give her a discount for quantity. The remarks went round Windy Nook and reached the police.
Leonard and Lawrence were exhumed and both contained phosphorus, from a proprietary beetle and rodent killer. Knowles and Russell were exhumed too and also contained it. She was tried at Leeds in March 1958 for the murders of Leonard and Lawrence, convicted, and sentenced to death. She was reprieved on account of her age, sixty-six, and died in Holloway prison on December 5, 1962. The press called her the Merry Widow of Windy Nook.