Mary is the girl who lived in Village XVIII in the Forest of Hands and Teeth, and was in love with Travis.
Mary grew up to stories of the ocean, told by her mother. Since then, Mary has always been fascinated by the ocean and was dedicacted and Returned.
Mary originally becomes a Sister, one of the leaders in the village, but she marrys Harry, Travis' brother.
Just before Harry and Mary get married, Village XVIII gets attacked by the unconsecrated. She, Harry, Travis, Cass, Beth and Jed escape and they walk down the forest while battling zombies.