|"The woman blinked. She was in her late thirties, Lyra supposed, perhaps a little older than Mrs. Coulter, with short black hair and red cheeks. She wore a white coat open over a green shirt and those blue canvas trousers so many people wore in this world."|
|The Subtle Knife (Knopf 84)|
Dr. Malone built a computer that acts similar to Lyra's alethiometer, in that it can communicate with Dust/Dark Matter/Shadow Particles, only on the screen; she calls this The Cave. When Lyra shows up and begins asking questions, a course of events is begun that will lead the ex-nun turned physicist through one of the windows between the worlds into the crossroads of Cittàgazze and finally into the world of the Mulefa, all the while guided by Dust through the ancient Chinese method of divination known as the I Ching.
It is her destiny, Dust tells her via the computer, to play the part of the serpent to Lyra in Pullman's retelling of the temptation and Fall of man.
Once in the new world, she befriends the peaceful Mulefa (notably the zalif known as Atal) and immerses herself in their culture. She learns their language and helps them in determining what is causing the Sraf (the Mulefa word for Dust) to be flowing away, as well as the decline of the massive seed pod trees (which put any redwood to shame) which the Mulefa use for transportation.
When Will and Lyra eventually turn up in the world of the Mulefa, hunting their dæmons, Mary follows the advice of a ghost, and fulfills her role as the serpent by telling them stories. When she returns to her own world (and agrees to help Will), the witch Serafina Pekkala teaches her to see her dæmon, an alpine chough. What her and Will's fates are, we are never told.