In 1986, she committed suicide, with the aid of her husband, in order to prevent her capture by the Templars who sought to use her to locate an Apple of Eden previously handled by one of her Assassin ancestors. After Mary's death, Joseph found himself unable to kill his and Mary’s son, and instead ordered Callum to flee before the arrival of the Templars led by Alan Rikkin. However, Joseph was taken and brought to the Abstergo Foundation.
Mary's death continued to haunt Callum for years to come, the young child having not understood to true reasons for her death. It was not until 2016, when he reunited with Joseph, that he came to terms with the circumstances of his mother's death.
- During the opening sequences of Assassin’s Creed: The Movie, Mary is shown to have died in 1986. However, later in the film her name is shown on a genealogical board with her date of death marked as 1988.
- During the scene of Callum and Joseph reuniting, a brief scene shows that Mary had held her husband's hidden blade and stabbed herself in the neck.