Sebastian has gone into the catacombs without waiting for you, Ominis, or Anne. It is unclear what he might be doing in there, especially in the name of curing Anne. Ominis has sensed Inferi, though… This isn’t looking good; you have to get in there and confront Sebastian.
As Ominis will tell you in his Owl message to you leading up to this quest, Sebastian has gone ahead of you, Ominis, and Anne, and entered the catacomb himself. Before you can follow, you will need to wait for Ominis and Anne to stop talking to each other (1), and then speak to Ominis (/)(2), which will open the door to the catacomb (3).
Before opening the door, Ominis will tell you that the catacomb is now crawling with inferi, which begs the question as to what, exactly, Sebastian is doing in there.
Defeat the Inferi
For the most part, you will be following the same path you took during In the Shadow of Time through these catacombs, only now you will be able to ignore most collectibles (assuming you grabbed them the first time through). The first room you come into will be clear of enemies, as well, though you should be prepared to face some inferi starting in the second room.
In the second room you come to, inferi will begin to rise from the floor as you approach. Thankfully, they will not become aware of you until they are fully above ground, giving you plenty of time to cast Disillusionment so you can sneak behind the inferi to take them out with Petrificus Totalus.
If you are spotted, though, taking out Inferi will require you to set them on fire first. Either use fire spells (Incendio, Confringo, Bombarda) or use Ancient Magic Throw to toss some exploding pots at them, setting them ablaze.
After taking out this first group of inferi, be prepared to take out make more in the next room, which will be crawling with inferi, many of which will respawn. Still, the antechamber is large enough that it is easy enough to get behind the inferi using Disillusionment so you can cast Petrificus Totalus on them, taking them out quickly.
After you take out the inferi and continue forward, Ominis will stop you to speak with you. He will express his concern over what Sebastian is planning, and will encourage you to hurry to get to him.
In the next room, down some stairs, there will be a few more inferi that you will need to take out before progressing. Using the same methods as before, you should be able to make quick work of them.
The previously-collapsed hallway in this room will now be clear, opening up a new path straight ahead. Following it down, you will soon come into sight of Sebastian, surrounded by seemingly-friendly inferi. Between you and him, however, will be a small bone staircase that you’ll need to construct.
To start, simply cast Revelio to see which Accio alcoves contain bones, then use Accio on the handles of both of the bone-holding doors (1 and 2). Most each of the piles of bones to the metal plate in front of you (3 and 4) in order to construct a stairway. Go up it (5) in order to come upon Sebastian, who you can speak to with / (6).
Speaking to Sebastian will cause a cutscene to play, after which will come a boss fight. Be ready!
Defend Yourself Against Solomon
After the cutscene, you will find yourself facing off against the enraged former auror, Solomon Sallow. This boss fight is fairly straightforward, and Solomon acts very similar to other human enemies, but he does have a lot of health, and will attack you alongside a small horde of inferi.
The best ways to defeat Solomon Sallow are to use Ancient Magic on Solomon Sallow as it builds up, and to juggle Solomon whenever possible (though he will escape juggles eventually). When you start to feel overwhelmed by inferi, you can use Ancient Magic Throw to launch fire pots at them, making them vulnerable and damaging several at once. Of course, keeping an eye out for attacks that you can use Protego/Stupefy on is also essential for getting through this slugfest.
After you defeat Solomon, a cutscene will play, revealing what Sebastian is willing to do for his sister.
After the cutscene, you can follow Sebastian out of the catacombs. Simply follow him, and he will use the same path you did for getting out.
Talk to Sebastian
Once outside, you’ll be able to confront Sebastian about what happened at the end of the battle with Solomon. After he explains himself, you will be given the option to learn Avada Kedavra, the killing curse. To do so, you just need to select the “Everyone should know that spell” dialog option, then agree to learn the spell.
Whatever you choose, you will complete In the Shadow of the Relic once you finish your conversation with Sebastian. Now all that is left is to determine what the consequences of his questline thus far will be.
Graves is an avid writer, web designer, and gamer, with more ideas than he could hope to achieve in a lifetime. But, armed with a mug of coffee and an overactive imagination, he’ll try. When he isn’t working on a creative project, he is painting miniatures, reading cheesy sci-fi novels, or making music.