The end happens fast: Ralph is pretty convinced he's about to die, when all of a sudden he rolls (literally) into a British naval officer who promises to rescue them. When we meet the officer, we get a quick look at the boys from his perspective; they're not wild savages but "little boys, their bodies streaked with colored clay, sharp sticks in their hands"; Ralph needs "a bath, a haircut, a nose-wipe, and a good deal of ointment" (12.224, 12.228). But it's all, according to the officer, "fun and games" (12.218-219).
Ralph tries to explain, but he doesn't get far. The officer interrupts him, saying, "I know. Jolly good show. Like the Coral Island" (12.247). (Coral Island? Check out our "In a Nutshell" to learn how Golding felt about that book.) In other words, he thinks that the group of boys is having a storybook adventure: no rules, no adults, and all fun. When Ralph starts weeping, the officer looks off into a "trim cruiser" resting in the distance (12.249), and that's when Golding hits us over the head—or, okay, taps us on the shoulder—with the real message: it's all savagery.
The officer represents civilization, but he also represents the horror of civilization: war. It might be cleaner—and the officer might not need his nose wiped—but it's no less savage. In fact, it might be more savage, because it hides behind "a white-topped cap […] a crown, an anchor, gold foliage" (12.215).
Rescue? Not quite. The boys may be getting off the island, but they're just going to grow up into soldiers destroying another Eden—only this time, the Eden is the whole world; and the "fire" is an atomic bomb.