Our hero, Joel Harrison Knox, is an imaginative (read: pathological liar) thirteen-year-old from New Orleans who's hit a rough patch. His mother has just died and, after living with his aunt Ellen for a while, he is sent to live with his father in Skully's Landing. Joel does a lot of growing up the summer that he moves, and the crazy circumstances of his new life require him to adapt in some pretty odd ways.
Other Voices, Other Rooms is about a really rough time in Joel's life. Not only is he hitting puberty (which is no fun for anybody) but also his mother has just died and he's being forced to move from the only city he's ever known to the middle of nowhere to live with a father he doesn't know. So Joel has to figure out some coping mechanisms to deal with all of this change. He gets through it by escaping into his imagination, knowing his enemies, and accepting his fate.
Joel's a storyteller, by which we mean huge liar. Like pants-on-fire levels of make believe. When Zoo, the cook at Skully's Landing, asks him if he's ever seen snow, he outright lies:
Rather breathlessly, Joel lied and claimed that he most certainly had; it was a pardonable deception, for he had a great yearning to see bona fide snow: next to owning the Koh-i-noor diamond, that was his ultimate secret wish. (1.2.87)
See what we mean?
Why does he do it? Well, it might be because the truth hurts too much. When he elaborates, telling Zoo about the time he and his mother were caught in a snowstorm and how she died before they were rescued, Zoo knows he's fibbing. He begs forgiveness but, later, when Jesus Fever is dying and feels cold, Joel says, "'Mama was always cold, too,'" (2.9.4). There's a bit of truth in his story about the snowstorm, but it's a much better story to tell than the painful truth.
Joel also plays lots of tricks on himself to try to escape the terror of his new life, mostly by remembering his old life. At the end of the novel he gives it one last shot, watching some clouds pass and:
[…] thinking that when they had, when he looked back, some magic would have taken place: perhaps he would find himself sitting on the curb of St. Deval Street, or studying next week's attractions outside the Nemo: why not? (3.12.56)
His imagination transports him—and the poor kid is in desperate need of transportation out of his weird new home.
While Joel is a young, fairly naïve kid, and doesn't understand everything that's going on at Skully's Landing, he knows it isn't right, and he's wary enough to never let his guard down with Amy and Randolph. When Randolph laughs about the time Zoo's husband attacked her, Joel protests:
"Keg cut her throat," said Joel, a mood of panic bubbling up, for he couldn't follow the peculiar turn Randolph's talk had taken; it was like trying to decipher some tale being told in a senseless foreign language, and he despised this left-out feeling, just when he'd begun to feel close to Randolph. "I saw her scar," he said, and all but shouted for attention, "that's what Keg did." (1.4.30)
This is where Joel realizes Amy and Randolph have no sympathy, and he adjusts.
After their totally callous talk about Zoo's assault, Joel sees that he's at the mercy of people that are a teensy bit bizarre. He starts complying to keep them happy. When Randolph says:
[…] in a voice as urgent as the bell, […] added "And please tell me what I want to hear," Joel remembered. "Everything," he said gently, "everything is going to be all right." (2.8.37).
Really he's just playing along, keeping Randolph happy until he can escape.
Even when he runs away, Joel knows how to buy himself time by buttering up the gruesome twosome. Amy and Randolph send him upstairs for wine and, before he takes off he sets "the bottle of sherry on the hall-tree in the chamber" (2.11.11). By fulfilling their request he keeps them happy and also keeps them liquored up, which will make it harder for them to even notice he's gone or come after him once they do.
Unfortunately, Joel's strategy of placating Amy and Randolph is not entirely successful. He isn't able to get away from them in the end, because he's afraid. When Miss Wisteria chases him through the old house he remembers that "[h]e owned a room, he had a bed, any minute now he would run from here, go to them" (2.11.29). Instead of escaping with Idabel he goes back to Skully's Landing. It seems that, for Joel, better the devil you know than the devil you don't.
The first thing we read from Joel's fever dream is that "He sentenced himself: he was guilty: his own hands set about to expedite the verdict" (3.12.1). Maybe he's guilty of having chosen to stay behind rather than run away with Idabel. He sentences himself to living a life of craziness and isolation rather than going out into the wide world.
Finally, at the end of the novel, Joel completely accepts his new life. The lady in Randolph's window beckons to him:
[…] he knew he must go: unafraid, not hesitating, he paused only at the garden's edge where, as though he'd forgotten something, he stopped and looked back at the bloomless, descending blue, at the boy he had left behind. (3.12.58)
Being unafraid is new for Joel, and indicates that he has transformed completely, accepting Randolph and Amy as family.
It's also heavily suggested that he's accepting something else: that he's gay. Remember, Joel is a little kid worried about not seeming masculine enough. He's really attracted to Idabel's masculinity. So he leaves his boyhood behind to follow his a man dressed in woman's clothing. In a sense he's retreating (he's leaving the natural world behind to go inside) and in a sense he's advancing towards the "rooms" that make up his real identity.