As The Accidental opens, the eccentric Smart family are spending the summer living in the "boring nowhere" of a bohemian, crumbling-down summerhouse in Northern Norfolk. Matriarch Eve Smart is far too preoccupied with writing her series of "Genuine Article" books, which detail the ordinary lives of real life Londoners killed before his or her time during the Second World War, to be concerned about her increasingly splintered family.

Eve's son Magnus has just tried to unsuccessfully hang himself in the bathroom, wretched over the part he played in a practical joke that resulted in the suicide of a school colleague. Her daughter Astrid is also living in her own private world of conceit. Armed with a new video camera, Astrid obsessively videos everything she sees, as though trying to make sense of a world constantly changing and evolving.

Michael, Eve's second husband, is too distracted by his own problems to take much notice of what his wife and stepchildren are doing. A pretentious, self-absorbed English literature professor, the reckless Mike is more concerned with bedding his array of preening female students, even having quickies with them behind the desk of his office, than with being a devoted husband and step-father.

One afternoon the mysterious and mercurial Amber arrives at the cottage, unrelentingly insinuating her self into the Smarts' lives. Amber is a gypsy, "salacious and rough looking, with her high-cut shorts and her low-cut shabby shirt," who sleeps in her car. Each member of the Smart family assumes she is a friend of the other; she is actually a skillfully charismatic freeloader who charms her way into people's houses, steadily taking advantage of their generosity.

This unruly girl immediately captivates Michael, Astrid, and Magnus. Eve, however, sees her as an "exotic fixative" - a charlatan, a trickster and a liar. Amber seduces Magnus in a church, where he sees her as broken, a "beautiful piece of something glinting, broken off the seabed, miraculously washed up on to the same shore." Astrid is besotted with the older girl's womanly and earthy ways, seeing her as a partner in crime, a new best friend. She even takes the blame when Amber suddenly throws her video camera off a motorway pedestrian bridge.

Multi-layered and packed with metaphor and meaning, The Accidental is highly experimental in form and structure. Author Ali Smith employs various narrative techniques to highlight the muddled world of the Smarts and their strange encounter with Amber. Her style is tentative and radical: short, sharp sentences emphasize the pounding stream of consciousness, the unremitting perception taking place in the characters' inner lives.

Ali Smith offers up a mostly compelling narrative, and the fact that none of the characters are even remotely likeable is part of the story's charm. But the author's brittle experimental style - the dialogue is often in sonnet strings, thoughts are introduced in point form, and words periodically disperse across the page - just becomes too irritatingly repetitive, often coming across as pretentious and affected.

Smith is tough on her characters as she unwraps the layers of a family mired in misunderstanding. Eve eventually wises up to this precocious girl who has the effrontery to turn up at their holiday house, eat their food, charm her children, and then tell what Eve suspects is the most blatant packs of lies she has ever heard. But the family's experience with Amber ultimately fails to lift them out of their moral quagmire and their fondness for miscommunication. The Smarts remain just as self-indulgent, hazy and blurred as before this inscrutable girl charmed her way into their messed-up lives.