Basically the "Big Thing" is the biggest part of Chapter 2, and the Swamp Camp is the Crux of this chapter.
If you joined the Old Camp or New Camp, either Raven or Mordrag will tell you that they want you to go over to the Sect Camp and find out what's up. If you have joined the Sect Camp, Cor Kalom will just tell you to go make yourself useful, and send you to deal with some weed makers outside the New Camp.
No matter which camp you joined, when you bump into Lester at the Main Gate, he will tell you he is glad you are here, and that the Brotherhood is planning to contact the Sleeper. He will tell you to go speak to Y'Berion in the temple. Go do this.