Contract: Deadly Delights is a Side Quest in Novigrad with suggested level 15.

Talk to the guard & choose the option "Let's talk about my pay". After talking to the guard, head to the medic to examine the bodies.

After talking to the medic to clues about what type of monster it is, head to the crime scene to investigate further.

Use your Witcher Senses at the crime scene to find hoof prints. Follow the hoof prints towards Crippled Kate's. Head into Crippled Kate's through the front door.

Talk to the Owner at Crippled Kate's, and she'll not want to talk about the murdered guards. After convincing her to tell you the truth, Geralt discovers its a succubus.

Go to the nearby house designated by your map marker. The room is on the second floor.

After confronting that it's the succubus, you can decide to kill her or let her live, but she must leave the city, and give you something that could be used as proof of her death.

If you kill her, you have a chance to get the Succubus Mutagen (needed for the Succubus Decoction). There are only two chances in the game to get it. It's not a must-have, but if you want to create all decoctions, you'll need to make the tough choice for one of the two.

Return to the guard, to collect your reward.