Contract: Doors Slamming Shut is a Side Quest in Novigrad.

This quest can be started at the quest board on Hierarch Square in Novigrad. From the quest board you must pick up the note that says "Contract: Haunted House". The "Doors Slamming Shut" witcher contract will then start automatically.

Go to the innkeep near the quest board and talk to the the man on the upper floor. He will send you to a mansion in Novigrad. Go to the basement and you will discover Therazane, a mighty elemental Boss Enemy. He will kill you in 2 hits and has an incredible amount of health for his level. He is resistant to almost everything. Always keep your Quen sign active.

The basic strategy for this boss fight is to attack Therazane with 1-2 strong attacks, then dodge back immediately when he starts an attack. He will miss you almost every time and if something goes wrong you still have your Quen sign to protect you from damage. Once you have learned his attack pattern the fight will be very doable, especially because he is a very slow enemy and easy to dodge. When you attack him too many times in a row he will go into a defensive positon. Don't attack him when he does that! He will block your attack and cause a massive explosion that has the potential to one-hit kill you.

Return to the quest giver once Therazane is defeated. Doing this will also unlock the Ashes to Ashes trophy / achievement.