Mary Flanagan was born in London on 9 June 1943 into a Catholic family of Irish descent, with her father's family originating from Pass, County Meath. She had two sisters, Eileen and Brenda, and a brother, Kevin. The family lived at Wallace Road, E15. Flanagan attended Holbrook Road Secondary School and, at the time of her disappearance, worked at the Tate & Lyle sugar refinery in Silvertown. She also occasionally worked at an opticians in Stratford and volunteered with the Blind Association.
In the weeks before her disappearance, family members later recalled that Mary had been seen frequently with a man introduced to her as "Tom," reportedly an Irish immigrant possibly connected to the Merchant Navy, though police have never been able to trace him. He may have been her fiancé, but details about him are limited and inconsistent; he has been referred to variously as McGinty, McEntee, or McGuinness, and the Merchant Navy had no record of a Tom McGinty in its service. Family members have speculated that Mary might have been pregnant, which would have been considered "a major thing for a 16-year-old Catholic to tell her parents" at the time. Her sister Brenda later described a bitter argument between Mary and McGinty, sparked by Mary's discovery that he had lied about living with a landlady when he actually lived with his mother. This dispute, involving raised voices between Mary, McGinty, and Mr Flanagan, reportedly left Mary distressed and led her to oversleep on the morning of 31 December; she had gone to bed in tears, telling her sisters she intended to end the relationship.
On 31 December 1959, Mary was due to attend her employer's annual New Year's Eve party at the Silvertown plant. She was last seen approaching West Ham tube station. The following day, her family realized she had not returned home and went to the sugar refinery seeking information, where they learned she had actually been absent from work for the previous two weeks — a fact Tate & Lyle had not flagged, having assumed she was off sick. A search involving both police and locals followed, with some local newspaper coverage, though the case was likely viewed at the time as a typical teenage runaway situation.
Police continued periodic checks of the National Insurance database, including in 1983 and subsequent years, but her National Insurance number has never been used for employment since her disappearance. In 2013, on what would have been her seventieth birthday, the Metropolitan Police and the Newham Missing Persons Unit reopened the case. The investigating officer described it as a "complete one-off" and it has been cited as an example of evolving policing methods over the decades. Police specifically appealed for information about "Tom McGinty." In January 2017, the charity Missing People commissioned a new age-progressed image of Mary from UK forensic artist Tim Widden.
Mary Flanagan, a 16-year-old Tate & Lyle employee from West Ham, disappeared on 31 December 1959 after leaving her family home and being last seen near West Ham tube station. Her case remains unsolved and has been described as the Metropolitan Police's oldest open missing person case.
