She is the village herbalist, and is also rumoured to mix with the dark arts. She is very skilled in torture, oration, magic and deceit, and apparently has the power to teleport and turn invisible.
Langiva has brainwashed many of the villagers into following the Pagan ways of human sacrifice and dark magic. Langiva seeks to depower the Christian God because then her religion will be all powerful. Langiva has loyal followers in the village, such as Hob, her bodyguard. However, Langiva can look after herself well enough and is only using the people as disposable cultists.
When Ulrich and his soldiers, together with a monk named Osmund, arrive from civilization to seek shelter and protection from the Black Death at Langiva's village, Langiva welcomes them even though she is suspicious of their nature. She drugs the men over supper to prove that she means business and she has the village's women seduce the men to try and get information out of their real quest.
However Ulrich's soldiers are more resistant yet wake up in the morning imprisoned. Langiva spares Osmund, showing him that his "deceased" girlfriend is in fact alive and in a hut in the village. Osmund, scared, goes into the hut to see his girlfriend stumbling about as if Undead. Terrified, he tries to comfort her that she is an abomination in God's eyes and kills her.
After Osmmund returns from the hut, Langiva scoffs at him that his girlfriend was never dead, only drugged, and the supposed murderers hadn't in fact killed her but badly wounded her. Langiva says she actually saved Osmund's girlfriend by bringing her to be healed, but Osmund is sure what he saw was a walking corpse and he condemns Langiva for dark sorcery. In response, Langiva has Ulrich killed by being wrenched apart by being chained to wild horses. Langiva is smiling through the assassination, showing acts like these give her more power.
Langiva escapes just as Ulrich's men attack the villagers, many of whom flee out into the wilderness, those that remain are killed. Hob is tortured about why he followed Langiva, he says "She was beautiful" and is then killed. Osmund follows Langiva into the swamp and pressures her for answers. She says he should ask God for answers, if God is really a good all-knowing deity. Langiva then mysteriously disappears and Osmund never meets her again.
However, she is the catalyst for Osmund becoming evil himself, he hunts down innocent women with a vengeance, and sees all women as witches after this. He tortures women brutally before killing them whether or not they confess, and Osmund sees all the innocent victims with Langiva's face.