The third quest in the Sebastian Sallow questline is In The Shadow of Discovery. This picks up right after the last and is a rather short quest with some important dialogue. For this quest, you won’t even need to leave the Hogwarts grounds to speak with Sebastian. The guide below goes over how to start and complete In The Shadow of Discovery in Hogwarts Legacy.
How to Start and Complete in The Shadow of Discovery in Hogwarts Legacy
For this quest, you will need to have completed the previous Sebastian Sallow quest In The Shadow of The Study. For this quest, you will need to use the wait feature on your map to get the next letter from Sebastian. Once you do, head to the Undercroft, which is located under the Defense Against The Dark Arts Classroom. When you enter, you will find Sebastian and Ominis in another argument, thanks to the use of Crucio in the previous quest.
Once they are done arguing, you will need to speak to Sebastian. It’s here that you can either support or condone his actions. This won’t have a major effect on the story. After he leaves, you will need to speak to Ominis and either defend or work with him to try to talk Sebastian out of using the unforgivable curses to try and help Anne.