I have 2 plots that I like, both around the same point in the story (but I'm not sure if they can go together), so which do you like more?
Whwre it starts: after a year of disappearing, a group reunites with an old friend, and just ignoring how it lead up to this point in this post, he's essentially lost it. He kidnaps his old friends who thought he was dead, brings them to his own little underground colony/ cult, and shows them around. His plan is to have them understand his distorted view of the world.
1st branch: the crazy friend doesn't appear to enjoy this life he's putting on, and just acts this way because he doesn't want his cult followers to kill them. He wants out, and tries to confide in his old friends to get him home. They don't really want to, because he's killed another one of their friends, but they do realize that this guy isn't all right in the head and needs help.
2nd branch: he kidnaps them, but actually enjoys his new cult life. He has a game in mind so they can share his view on the world (it involves drastically distorting their choices, lifestyle, making them feel unimportant, etc.) He let's them go, so he can follow them to their homes, find their colony, and wreak havoc on everyone.
The first choice would involve more of the underground cult setting and kind of a jailbreak story, and the 2nd would be more of the groups colony and the cult leaders manipulation of events, and assuming control over their lives.
Worth knowing, this cult leader isn't actually a good character either way. He has somewhat good goals (from his pov) and each choice is still a way to get to their colony, that he doesn't know how to get to, do to some memory trauma. One is just more blunt (following them) and the other is more sociopathic (garnering sympathy and getting them to instate him in a colony sanitarium, which he would later escape after putting on a facade).