There isn't a clear delineation between Part 1 and Part 2 as the chapters continue without a break in the story. However, part 2 does go further into the cult-like brainwashing that is rampant throughout the island, and we see Male Character A being trained into submission. Once again, this story should probably include the tag "Drug Use." The sex scenes in this part of the story almost entirely (if not entirely) involve coercion, manipulation, and force.
There are multiple power shifts and the true purpose of this island is revealed, and then later the true true purpose of the island is revealed. And honestly the true true purpose of the island doesn't seem all that different from the original purpose of the island (prostitution), so I'm left feeling that all the intrigue and shit was just the author trying to go through the motions of writing a plotline but not caring enough to actually put thought into it. And I'm not sure when Male Character A had the time to build that boat out of plastic bottles. It seemed to be added at the last minute since they needed an escape vessel. The main purpose was just to have a series of sex scenes loosely connected by a "plot."