She sneaks out without her family's knowledge and not only goes to the fair, but later on that night kisses and eventually makes love to Dennis, which we later learn, results in pregnancy.

Even though Mary was only seventeen, there would have been no legal problem with her marriage since the English law which, until 1970, generally required people under twenty-one to have parental consent to marry, did not apply in Scotland.

Mrs. Brodie stumbles into Mary's room and begins to scream at the fact that her daughter is with child, and calls James himself to sort it out.

In the third part of the book, Brodie forces Nessie to study hard so as to win the "Latta", a valuable bursarship.

Under his threats and the dreadful fear of failure, she labours on with it, making herself mentally and physically ill. Nessie secretly writes to Mary asking her to come back, so she will have her company and comfort.

Finding that her rival has won it and fearing her father, she sends Mary out to the chemist on the pretext of getting some medicine, then dresses up and hangs herself.