Chapter 12 is the last part of the novel, and at this point Ralph is completely alone; all of his friends and allies are either dead, or have sided with Jack. Samneric were the last surviving members of Ralph's group, and they were captured by Jack the previous day. Now, scouting Castle Rock, Ralph sees that Samneric have been put on guard duty, evidently having joined Jack's tribe.
Ralph attempts to sneak up on Samneric to convince them to run away with him, but they turn against him, threatening him and saying that he needs to go; that the next day, Jack is planning a hunt for Ralph. What's worse, (and Ralph doesn't understand the significance of this), Jack has Roger prepare a stick sharpened at both ends. The horrible implication is that the boys are not only going to kill Ralph, but behead him, mount his head on the stick as an offering to the Beast, and even possibly eat him.