The password to his email is “gravity” (note the poster on the wall). At this point you can access his computer. He’ll say some threatening things and then escape, leaving you alone. He’ll attack you with an axe, and once you get him to half health, he’ll disappear again. If you follow through, then you have a brief combat with Gary.
If you don’t tell him this or you renege on your threats, then you fail your trial and you cannot join the Sabbat.
After he appears, you can tell him you’re going to kill him for the Sabbat. When you get to Gary’s lair, then things change. You can talk to Imalia and Mitnick and get their quests. Everything should still be normal at this point. Your reward: Andrei will allow you to skip several of the sewer maps and brings you to the final map, the one that takes you to the Nosferatu hideout. If you agree to all this then you’ve started your initiation in to the Sabbat. If you follow through and agree with him, he will receive you into the Sabbat, but not before you prove your loyalty: Andrei will ask you to continue on through the Warrens to kill Gary rather than to simply find him and discuss the sarcophagus.
During your conversation, there will be several opportunities in the dialog to ask Andrei about his plan and joining the Sabbat. The Sabbat content becomes available first after speaking with Andrei during the King’s Way quest, when Isaac sends you to Andrei’s house to kill him.
