Leandra, also known as the Conduit, is the leader of the Immaculates.
She is the sister of Icara (also known as the White Witch) and they got soul forged as children when they witnessed their parents' murder. Both girls lived a solitary life in Luculla forest, caring for the animals and dealing with others quite seldom.
The arrival of the Wizard Zandalor marks a dramatic change in the girls' lives, his kind nature had an immediate effect on Leandra and Icara. Being soulforged, the sisters were painfully aware of each other's feelings for the wizard. When Zandalor confesses his love for Icara, they decide to tell Leandra together. Upon hearing the news, Leandra fled their home, heartbroken.
In her time of weakness, she is approached by the Trife and seduced by the notion of a peaceful non-existence for all, offered by the Void Dragon. It is then that Leandra takes on the guise of the Conduit. With the sisters' soulforge mangled, Leandra quickly spirals downward, leaving destruction and slaughter in her wake.
In pursuit of her goals, Leandra enters a deal with King Boreas. She provides him with an elemental staff capable of imprisoning his brothers, in exchange for his Star Stone, the lives of his imp workers (their blood is used to fuel more Blood Stones) and the incarceration of her sister Icara.
The town of Hunter's Edge is sacked by orcs and mountainmen at Leandra's behest. Almost everyone is cut down in order to create more Blood Stones. Several of the villagers are reanimated and forced to work in a tenebrium mine, gathering the toxic ore used to construct Leandra's death knights.
At the final battle, you can choose between repairing the Soul Forge between Leandra and Icara or just leaving it mangled. If you choose to leave it cut, you will have to fight Leandra during the final battle with the Void Dragon. She summons Death Knights, and has two unique Death Knights, Death Princes, who guard her during the fight.
If you choose to restore the Soul Forge, Leandra comes to her senses and trembles thinking about what she had done. You need to get Soulforge Repair Ritual in advance to entering the First Garden. After confirming that her rationality has returned, Icara and Zandalor teleport with her, so you don't have to fight with her at the final battle.