Briony Tallis, thirteen-year-old dreamer and interferer, is a very useful character for you. That's because when your parents tell you to clean your room you can say, "Hey—you don't want me to be like Briony, do you? You want me to clean my room and then destroy my sister's life and bring sadness and woe to the entire family?? I didn't think so."
Obviously, this will work better if you actually have a sister. Okay, it probably won't work all that well even then. But still—it's worth a try, right?
Even if she won't get you out of cleaning your own room, though, Briony definitely cleaned her own. One of the very first things we learn about her is that "She was one of those children possessed by a desire to have the world just so" (1.1.4). So much so, in fact, that in the entire upstairs of her family's enormous house, her bedroom is the "only tidy […] room" (1.1.4).
Briony's passion for neatness is where her love for writing and creation comes from. In stories, you see, she can control everything—she gets to tie off all the loose ends and make sure everything fits. She's at first enthralled with the idea of writing plays because "a universe reduced to what was said in it was tidiness indeed" (1.1.10). Eventually though, she realizes that putting on a play means dealing with other people's messes—literally in the case of her cousin Jackson, whose bed wetting interferes with rehearsals.
It's not just other people's pee that puts Briony off, though—it's other people's thoughts as well. Briony likes the idea of a world controlled by her own thoughts and imagination. A world in which everybody has their own thoughts and imagination, though, is… well, it's a mess, with "two billion voices and everyone's thoughts striving in equal importance" (1.3.18) and it "offended her sense of order" (1.3.18). When Briony reads Robbie's letter to her sister, it's not so much his expression of sexual desire that horrifies her as the recognition that he has an imagination and self. When she says she "could never forgive Robbie his disgusting mind" (1.10.6), It's not clear which seems worse to her—his mind or how he's using it.
Briony's accusation of rape against Robbie is also a product of her sense of order. She doesn't actually see Robbie assault her cousin, Lola, but "everything fitted; the terrible present fulfilled the recent past" (1.13.49). Briony has both a story and a reality. In the story, Robbie is a sex maniac with a disgusting mind; in reality, Lola is raped by a nondescript figure. When Briony combines the story with the reality, they come together pretty easily to form a tidy tale about Robbie's ruthless attack on Lola. No mess here, folks, just as Briony likes it.
Even as a child, though, Briony realizes that a world in which she is the only person with a consciousness would have its downsides. It would be neat, but also "sinister and lonely, as well as unlikely" (1.3.18). When she sees Cecilia take off her clothes and dive into the fountain in front of Robbie, Briony is excited and inspired precisely because she has the sense that there are other people and other minds out there; she's not alone. Her first long story, based on her vision of Cecilia and Robbie at the fountain, is based on a "pure geometry," but also on "the defining uncertainty which reflected, she thought, a modern sensibility." With some triumph she concludes, "The age of clear answers was over" (3.23). Growing up, in other words, is to accept messiness. It's also something Briony's eager to do.
Or is it? Briony's job as a nurse isn't to accept mess, after all; it's to scour bedpans and clean and clean and clean until everything is more sparkling and ship-shape than her bedroom ever was. Learning to be a nurse is a "narrowing" (3.13). Briony doesn't expand her consciousness to include others, but instead erases her own interior life, turning from Briony Tallis into Nurse Tallis—no first name, nothing special.
But what about Briony's writing? She's still writing after all, even after assuming her nurse identity. Her writing has changed, though, and the editor who rejects her story tells her it lacks "the backbone of a story" (3.226). He quite literally wants her to tidy the piece up.
The problem for Briony is that her effort to clean up messes in childhood created a huge, whopping, massive, gargantuan mess to end all messes—like if you tried to clean your room and accidentally dumped the mop-water on the bed and vomited in the closet. Only worse. In trying to fit Robbie and Cecilia into her own story of Robbie and Cecilia, she ended up sending Robbie to prison for a crime he didn't commit and destroying Cecilia's life. Learning to clean up messes as a nurse isn't going to fix that. Learning to accept messy stories in which nothing much happens isn't going to help either. Nothing's going to sort that mess out. It's more unfixable than an old chocolate stain on your favorite white tee shirt.
Yet Briony does fix the mess she made of Robbie and Cecilia's lives… at least she tries to. In the last section of the book, written by Briony on her 77th birthday, we learn that she has made a novel out of the mess—the novel we've just read.
The whole mess is back in Briony's head again, ordered and in place. She has fictionalized the messier components to resolve the tale neatly, including having Cecilia and Robbie not only live, but live happily ever after. She calls the earlier drafts—in which Robbie and Cecilia died like they did in real life—"pitiless" (4.45). We might call them authentically messy, but that's just us.
Briony is dying of vascular dementia at this point. The disease will slowly destroy her memory and consciousness before she dies, and she faces "an incoming tide of forgetting and then oblivion" (4.45). She'll be gone and the book will survive, carrying its tidy ending forward.
There's a bit of a trick going on here though. By telling us that the clean ending isn't real, Briony makes a bit of a mess. While asserting that an author has "absolute power of deciding outcomes" (4.46), Briony undermines her own fix. It's an interesting moment.
Which is all a round-about way of telling you to go clean your room… or at least shove everything under your bed so the mess isn't so glaringly obvious.