Marlie is one of the adults who volunteer to brave the Mountain and restore the stream to Rin. Before leaving on their quest she and Jonn, along with Rowan who brings cheeses as a gift, go to Sheba's hut to ask her for advice (as per Marlie's suggestion). The visit does not go as planned (or so it seems), with the old wise woman mocking the two adults, reciting a strange rhyme and throwing a stick at Rowan's head. Marlie is left feeling disappointed, until it is discovered that the stick is really a map of the Mountain which only Rowan can hold and read.
In the swamp on the Mountain Marlie is affected by the enchantment there, and feels as if spirits are touching her everywhere. She tries to help free Bronden who has run into the sucking mud after seeing an illusion of a loved one, but is almost sucked in herself. It is thanks to Allun that she (and Bronden) are not pulled underneath the mud, for Allun heard Marlie's cries and immediately came to help her. Later he tells her and Rowan that it was her cries which cleared and sharpened his mind again.
Later, after Bronden and Val leave the group Marlie asks Allun to sing for them as they walk, to keep their spirits up. Marlie is distraught when Allun reveals that he can't swim and thus can't accompany them further on their quest (as their path is blocked by water and they must swim to get past it). She embraces Allun with tears in her eyes before moving on with the others.
When she, Jonn and Rowan are forced to crawl through a small and cramped tunnel it is finally revealed that she is claustrophobic. Unable to stand being in so small a space, she rejoins Allun (who stayed waiting for them at the mouth of the cave) and they travel back together to Rin. Before they leave they gather up some Mountain Berries which Allun has found to take with them.
As Rowan and Jonn are swept back to Rin by the restored stream, Marlie can be seen beside Allun, cheering and smiling happily.
Marlie has married Allun and is now pregnant with his child. After the village is attacked by the Ice Creepers she leaves along with the others for Maris, despite being heavily with child. After seeing Zeel's kite and fearing that the village is in danger they turn back, however.