Contract: The White Lady is a Novigrad side quest. It has a suggested level of 16.

Talk to the widow to start the quest. You can increase your reward.

Head to the designated map marker location, then use your witcher senses to find the dead bodies. After examining two-three bodies, Geralt will determine that The White Lady is a Noonwraith. Near the dead bodies, there will be some tracks leading away from the other bodies. Use witcher senses and follow the tracks. The tracks lead to a broken tower. Bloodstains lead to the cellar of the tower. There will be another body there.

Head back to the widow to find something to draw the Noonwraith out. After talking to the widow, she will give you a dagger.

Head back to the campsite which is near the dead bodies. Be sure to use "Spectre Oil" beforehand, and use Yrden sign, to make your fight easier. Wait at the campsite until its day time, and the Noonwraith will appear.

After dealing with the Noonwraith, head book to the widow to collect your reward.