Mary Horsley

Mary was the wife of Isambard Kingdom Brunel. In an alternate timeline, Mary was killed in 1843 when the use of the Utopian Engine caused most life on Earth was accelerated by forty years in a matter of seconds. When Isambard Brunel learned what happened to his family from the Eighth Doctor, he wept for Mary and his children and the Doctor told him that he was sorry. (PROSE: Reckless Engineering)

Behind the scenes
In Reckless Engineering, Brunel's wife is referred to only by her first name. The title "Mary Horsley" is a conjectural title based on the real world name of his wife, in order to disambiguate her with another character known only as Mary who appears in the same novel.