The second part of the quest Contract: Devil by the Well. Geralt first brews some Swallow potions and some Specter Oil, then burns the remains and the bracelet to force the Noonwraith to appear and fight him. At certain points during battle the Noonwraith splits into three separate ghosts and these must be knocked-out to make it reappear again. The longer the battle goes on, the more this will happen.
Video: Devil by the Well Part 2
The Witcher 3 Guide 