The residents of White Orchard have suffered more than their fair share of misfortune. Passing armies had trammeled [sic] their spring planting, a griffin had begun abducting their livestock, and, the rotten icing on this painful cake, a noonwraith haunted a nearby well. No wonder the locals called this final evil a 'devil'. The witcher could sense something bound her to this place, and that in order to send her off into ethereal realms he would first need to learn her secret.
Once that was done, he would have to prepare for battle – and a noonwraith is a demanding opponent. She can disorient her victim by blinding him and creating mirror images of herself. These copies suck their victim's life energy – while their mistress remains untouchable. In order to defeat her, the witcher could not rely on his silver sword alone – the Yrden sign would also be needed to trap her and force her to take on material form.
Witchers don't normally feel a limited range of emotions regarding the monsters they slay. They despise the particularly cruel ones and are repulsed by the disgusting ones, but rare indeed is the monster for which they feel sympathy. Yet that is exactly what Geralt felt for the noonwraith of White Orchard. For a long time he was haunted by thoughts of the young woman whose horrible death and powerful emotions had transformed her into that terrible monster.
After reporting completion of the task to Odolan, you can talk to Tomira and learn that she knew the woman who has become the noonwraith, Claer. It is revealed that Claer insulted the lord by pointing out his dead son's Florian's sexual orientation (he and local hunter Mislav were close). This infuriated the lord and led to massacre.