Death by Fire is a smal and quick Side Quest in Velen. Travel North of Hanged Man's Tree and take the path on the right to a small house.

Death by Fire Walkthrough

When you arrive at the house you will notice smoke and fire coming from the house with someone screaming inside. You will also notice some bandits outside guarding the burning house.

Kill the bandits through heavy strikes with your sword, use Axii to stun them and get critical hits. Once you've killed the bandits use your telekinectic blast to clear the blockage at the door. An elf will run out of the burning house, speak to her and she will reward you with her secret stash. It is located behind the house in a wooden log.