Aislinn Kelly should be really annoying, but isn't; and this is such a great trick, it makes you wonder how she walks the high wire of our sympathy. She is the narrator of the latest book by Gwendoline Riley, a writer who likes to keep things close. Riley gives us first-person narratives from people who are a lot like her, being writers and drifters; young women who don't quite know what is wrong with them, or whether they want to put it right. Nonchalance and authenticity are almost the same thing here, though both words are a little strong, in the circumstances. Riley keeps her sentences smart, affectless and most wonderfully flat.

Nothing much happens to Aislinn over the course of this novel. She talks about her stupid, creepy father, fights with her American boyfriend, has conversations with friends, and goes to her mother's retirement party. She also spends some time in Indianapolis, writing. The dialogue is the opposite of sparkling. Aislinn's father uses "er" as a weapon and the off-the-beat use of italics reads like a threat. He sends a series of unanswerable emails to Aislinn when she is at college, one in response to her first book: "Oh dear! Oof! Posing! Er, what?"

Her stepdad is no great shakes either, with his bad clothes and insistence on speaking in funny voices. Her mother thinks of emotion as something that happens to other people: "Oh no I didn't feel anything," she says about viewing the dead bodies of her own parents. "No, nothing. Not with either of them."

Though she loves the way they talk, friends do not provide Aislinn with much respite. There is the miserable, "more or less  inanimate" Bronagh, who "used somehow to seep into my vicinity, when I was feeling low". A college roommate, Cathy, seems a decent sort, but she also starts to grate  perhaps it is the clothes, or the religious inclinations.

A couple of male friends are unproblematic, if not always fragrant, and there is the American boyfriend Jim, a singer-songwriter. Jim and Aislinn have a fight walking down the street, and his final insult, "like he'd found the right spot at last, the magic button", is that she is "'too literary'  And he couldn't even pronounce it: 'too litter-y' he kept saying, 'too litter-y'." This anecdote elicits one of the most apt responses to the figure of the critic ever penned, as her friend Karl says, "My God. Why didn't he just shit in your head?"

A first-person narrative is by nature self-enclosed. Any small narcissism puts us back on the outside; we become alert to signs of "vanity" and "self-pity"; we reject the narrator who enjoys introspection in the "wrong" way. This seems to apply, rather unfairly, more to women narrators than to men. There can be no mirrors in a book like this, and Riley manages the bargain very well. Even the slips she makes are salutary. "I don't really do food," Aislinn says, provoking an irritation from this reviewer  whether as eater or mother, I was not sure, but realising, in my uncertainty, that reading is close to nurture, in its intimacy.

The guys in Jim's band always had "such a crush" on Aislinn, "this English author", and we suspect she is good-looking, though this is never said. Opposed Positions is not a book about rejection so much as dissatisfaction. Aislinn is not like the heroines of Jean Rhys, who dress their desire in a ghastly hat, put the wrong man in front of it, and wait to be turned down. She is not unwanted, just complicated, in some way that is hard to describe: "when it came to sex, I mean  the truth was I had no impulses in that direction back then. No impulses at all."

And though she hasn't slept with Jim for some years, she does have sex with a guy  "pretty fit, as it goes"  towards the end of the book. "I have very little memory of sleeping with him, though." Trying to explain, she reaches for a quote from Philip Roth: "I can not afford the luxury of a self." Writing is an attempt to locate that self, through "some process of triangulation". This is an urgent task and there is a real sense of personal risk in these pages, a huge investment in getting the words right.

I am not sure Riley needs Philip Roth when she has Gwendoline Riley, a woman who shows herself more than up to the job of writing the wasted hinterlands of the human heart. Opposed Positions is also an enjoyable book. A narrator who should be irritating for being self-involved manages to be intriguing and sad. Aislinn Kelly is cool. She is smart, and accurate, she can write a dynamite sentence that manages to sound entirely bland. She has an eye for the flip and the sarcastic, she observes, maintains distance, doesn't put out. She brings nothing to the party, except herself, but she's the girl you remember, over in the corner, not drinking much.

 Anne Enright's latest novel is The Forgotten Waltz (Vintage).