When Wil Ohmsford, Amberle Elessedil, and the Rover girl Eretria find the location of the Bloodfire within Safehold, Mallenroh and Morag appear. They are apparently there guarding the power of the Bloodfire for themselves. They taunt each of the trio and do their best to cast doubts in the minds of the three travelers in an effort to turn them against each other.
They are almost successful: Amberle and Eretria start arguing and threatening each other. However, when Eretria's hand gets stabbed and her blood shows the way to unlock the Bloodfire, the two snap out of it.
Mallenroh and Morag recognize Amberle as the bearer of the Ellcrys' seed, and they try to stop Amberle from entering the Bloodfire. However, they are stopped by Wil, who kills them both easily using the Elfstones.
Changes made for the TV Adaptation
- Mallenroh and Morag are guardians of the Bloodfire in Safehold; in The Elfstones of Shannara they are the Witch Sisters, the last of their coven, and living in the Hollows, a region in the Wilderun where Safehold is found.
- Mallenroh and Morag are killed fairly quickly by Wil, with the use of the Elfstones. In Elfstones, Mallenroh is so powerful a witch that with no apparent effort she is able to keep Wil from even attempting to use the Elfstones against her. Mallenroh and Morag end up dying together in a fire caused by a magic duel they were engaged in.
Mallenroh and Morag live in the Hollows within the Wilderun; Mallenroh controls the west, Morag the east. Their domain surrounds the mountain Spire's Reach, location of Safehold and the fountain of the Bloodfire, the destination that Wil Ohmsford and Amberle Elessedil are seeking. Although their magic is immensely powerful they have no power outside the Hollows, in the manner of the King of the Silver River, indicating that their magic is an earth magic tied to the land and perhaps to the Bloodfire itself.
The Witch Sisters have been locked in bitter struggle for centuries, with powers so evenly matched that neither has been able to gain the upper hand over the other. The old man Hebel tells Wil and Amberle their original dispute was over a man who was killed during their struggle; this is later confirmed by the witches, although it is unclear which one is responsible for the man's death.
Mallenroh's minions — magically animated stickmen — capture Amberle and later lead Wil, Hebel, and the Rover girl Eretria to Mallenroh's tower. It becomes apparent that the witch enjoys collecting "pretty things," whether that be jewels, carvings, or people, including Eretria and the man she and Morag fought over.
When she meets the travelers, Mallenroh turns Hebel and his dog Drifter into wooden figures and takes the Elfstones from Wil. When Wil points out that the Elfstones only work for those with Elven blood, Mallenroh claims to be of a race older than even the Elves, from the time of Faerie, and that as such the blood of all the Races runs in her veins. She imprisons Wil and Eretria in the cell where she is keeping Amberle.
Attracted by the power of the Elfstones and the potential they have to tip the balance in the Sisters' struggle, Morag comes to visit her sister and demands that she hand the over the stones. The Witch Sisters end up killing each other in combat when the magic fire they had been using to battle each other ends up setting Mallenroh's tower ablaze with normal, everyday fire. They are caught in the conflagration and burned to death.
Wil, Amberle, and Eretria free themselves during this battle with the assistance of Mallenroh's servant Wisp, a modified creature that was once an Elf. With his help, they recover the Elfstones and escape from the burning tower.
Centuries later, members of the Ohmsford family do battle with a warlock called the Morgawr, who claims to be a brother to Mallenroh and Morag.