"Mother" is a mysterious root kept in a metal box in the Abbey. It is revealed in Ectogenesis that "Mother" comes from the only tree on the island that is immune to the RFG fungus, having actually absorbed the fungus. "She" is said to be a "cure" for the virus.
Sister Anne claims that Mother is capable of providing a cure for the RFG. However upon going to get her, Sister Anne is distraught to discover that "Mother is missing."
Julia Walker tells Sister Amy that she needs Mother, and Sister Amy lies, stating she has Mother. Sister Anne reveals to Julia that only three people had access to Mother: Landry, Brother Michael, and Sister Anne. Landry has kept Mother safe up in an observation tower in the Abbey and Sister Amy and Sergio break in, and while the two boys are fighting, Sister Amy swoops in and steals Mother and delivers it to Julia Walker in exchange for immortality.
Upon being given immortality, Sister Amy finally reveals Mother's location to Julia Walker, who finds Mother and starts heading back to the Abbey, just as the military is spreading harsh chemicals to kill everything on the island. Sarah run outside and helps Julia after she falls to the ground. Julia reveals that the gas got to Mother, pulling out a blackened, petrified root.
Julia Walker hasn't given up trying to find Mother. Discovering a painting of Mother, she asks Sister Anne where the tree was once located and is intent on finding her to try and prevent anther NARVIK outbreak. Julia and Alan Farragut trace the stars in the painting with the stars in the sky above the Abbey and discover that Mother is IN the Abbey. Julia and Alan discover that the stump where Mother used to be is in fact underneath the Abbey, having pulled up the floor where Brother Michael would give "Counseling". After running some tests, Julia confirms that the stump and roots running underneath the Abbey are dead, however the fungus that it "absorbed" leaked into the soil and "Mother is everywhere."